The catch with the 3.5% p.a. at Trading212 (?)

Some time ago at Trading212 you got 3.0% p.a. on uninvested balances, now even 3.5%. A deadline, as with current account accounts, was not mentioned. I was already wondering where the catch was - now I think I've found it. To date, my assets have been invested in banks (J.P. Morgan, Helaba). Everything was fine until then because these shares were protected by deposit insurance. But now a new point has emerged. An amount larger than my previous amount