Wasn’t he aware that’s he’s a target for an assassination? Great Oscar did mention young Oscar was aware that someone close enough to be around him was the cause of his magic circle being sealed, likely to prevent the white tower from standing up again due to him being a genius. -> so he can’t trust anyone, since anyone is a suspect. Esp since considering they even found out Oscar buying a potion in secret.
Also Him gaining any source of attention from success ( business, theory etc)will likely result in his death since he has no magic to protect himself. Hence why he studied in secrets. Great Oscar also mentioned his behaviour(bad behaviour, slacking, etc) was a purposeful mask, likely to protect his life. The tower master were likely expecting him to have a result (before the reveal of him being unable to use magic) my guess is that Oscar invested in business to fail to completely destroy the hope and expectations of others so his act is more successful, that or he could just be a terrible businessman lol his talent lies in magic after all
If og Oscar is really that much of a genius, then is it really his fault that all his businesses and projects fail? Yes, just because you're a genius doesn't mean that you're a good businessman. But to fail spectacularly? Bet the people who want him dead did something to block him at every turn.
Unfortunately, one thing that this genius lack was human connection. Yes, he didn't trust anyone because of the blocked mana thing, but to not even try asking for help?