This is a long shot because I remember very little. I think I only read a few chapters. I could have sworn I save it to my reading/to read lists, but I can't find it in there.
From what I recall:
-definitely a manhwa, full colour
-extremely high production art, on the level of The Villainess is a Marionette or The Villainess Turns the Hourglass
-it was a regression story set in a medieval European setting, but it wasn't as generic as usual. I think it was slightly more actual high/late medieval Italy(?)/France(?)/Britain(?) in setting rather than the pseudo-Renaissance Europeland that's typical
-female protagonist, and I think she regresses to being a teenager. She's definitely unmarried at the beginning of the regression
-She's a noble and she lives in somewhere either with stone castle walls around the town, or it's a castle rather than a manor.
-there's a luncheon scene outside in a garden with a long rectangular table where she very politely and in political speak tells the higher ranking ml to fuck off after I think everyone else was ordered to leave? He may have been subtly proposing marriage or something? And maybe she took offense at how it seemed like a whim?
-she has a much younger brother in his tweens or early teens, but I can't remember if her parents are alive or if there's a regent or something. They have a fairly good relationship at least several chapters into the post-regression timeline. He's definitely at least a foot shorter than her
-I think there was a scene where the ml arrives on a horse and bumps into her on a dirtpath near a wall a ways away from town. and then the younger brother comes running up and stands in front of her facing the male lead? Or perhaps the younger brother bumps into the male lead first, and they go separate ways without much talking, and then the male lead bumps into the female protagonist
-I don't think there was magic, but I can't be sure
-there's a chance that there was something about her younger brother being raised separately in the first regression and being unable to read and something something her letters were misconstrued/intercepted? I'm not sure about that one; that might be a different manhwa
-I think there was something important to do with gloves? Something about social etiquette
-I don't think there was anything tropey like "male lead" or "fiance" in the title? I can't be sure
Yeah, so it's a lot of vagaries. I've been trying to find this for months, so any help would be appreciated.
I can't remember the name, but key points include:
-the tower was a way of making heroes to repel against an invasion of earth by some sort of cthulhu/evangelion monsters. no one involved knew this.
-after they exited the tower, they were unable to grow any stronger.
-the tower had 3 levels: easy, medium, and difficult. The difficulty could be chosen upon entry to the tower, and the more difficult the mode the stronger the survivors were upon exit. they did not know this at the beginning.
-whilst in the tower, they could talk to each other using some sort of forum. the mc did this on his second regression so he could share tips and hopefully increase the number of survivors.
-the mc chose easy the first time, but difficult the second time. the difficult mode gives each person their own tower without other humans in it. other modes involve a shared map of sorts.
-at certain defined points in the tower, the humans exit the tower back to earth and must repel monster invasions before being transported again to the tower.
Any help finding this would be appreciated. I have too many bookmarks and too few notes. Thank you.
Replying because I found it, but I keep forgetting: https://www.mangago.zone/read-manga/leveling_up_with_skills/
It's a villainess manhwa set at the ending of the story. The villainess avoided the death flags by befriending the heroine and marrying the 2nd male lead. It's the villainess' wedding day, and she has to get married at a specific castle on a specific day for some reason or she'll die. Her fiance runs off with the heroine, and the villainess has to find someone new to marry immediately. She marries someone else, and the fiance is salty about it for ages, which is the point. Something something revenge?
I don't think I read too far into it. If anyone knows which manhwa this is, it would be appreciated if you would let me know. Thanks.

This is a long shot because I remember very little. I think I only read a few chapters. I could have sworn I save it to my reading/to read lists, but I can't find it in there.
From what I recall:
-definitely a manhwa, full colour
-extremely high production art, on the level of The Villainess is a Marionette or The Villainess Turns the Hourglass
-it was a regression story set in a medieval European setting, but it wasn't as generic as usual. I think it was slightly more actual high/late medieval Italy(?)/France(?)/Britain(?) in setting rather than the pseudo-Renaissance Europeland that's typical
-female protagonist, and I think she regresses to being a teenager. She's definitely unmarried at the beginning of the regression
-She's a noble and she lives in somewhere either with stone castle walls around the town, or it's a castle rather than a manor.
-there's a luncheon scene outside in a garden with a long rectangular table where she very politely and in political speak tells the higher ranking ml to fuck off after I think everyone else was ordered to leave? He may have been subtly proposing marriage or something? And maybe she took offense at how it seemed like a whim?
-she has a much younger brother in his tweens or early teens, but I can't remember if her parents are alive or if there's a regent or something. They have a fairly good relationship at least several chapters into the post-regression timeline. He's definitely at least a foot shorter than her
-I think there was a scene where the ml arrives on a horse and bumps into her on a dirtpath near a wall a ways away from town. and then the younger brother comes running up and stands in front of her facing the male lead? Or perhaps the younger brother bumps into the male lead first, and they go separate ways without much talking, and then the male lead bumps into the female protagonist
-I don't think there was magic, but I can't be sure
-there's a chance that there was something about her younger brother being raised separately in the first regression and being unable to read and something something her letters were misconstrued/intercepted? I'm not sure about that one; that might be a different manhwa
-I think there was something important to do with gloves? Something about social etiquette
-I don't think there was anything tropey like "male lead" or "fiance" in the title? I can't be sure
Yeah, so it's a lot of vagaries. I've been trying to find this for months, so any help would be appreciated.
I think I know this, wait--
Was it this one, https://www.mangago.zone/read-manga/the_stone_thrown_in_the_lake/, nulla?
Yes, I think that's it! Thanks so much.