IBKR even has a SIPC excess insurance to cover USD 30 Mio. per account but with a total limit of USD 150 Mio. I assume this is mainly to cover fraud affecting a limited number of accounts.
As customer assets are segregated, the risk should be very low, even when investing beyond the insured amount, even if IBKR were to go bankrupt. Multiple accounts at the same broker for a single person don’t provide any advantages (except if one account is hacked and another isn’t, I suppose).
If you don’t feel safe enough at a single broker, you need to open an account at a different broker. While I do have accounts at two brokers, I consider the risk of a permanent loss of invested securities due to bankruptcy very low at Interactive Brokers.