On Binance Smart Chain, owning bnb but insufficient funds

Hi everyone,
I sent bnb from binance to metamask on Binance Smart Chain network. I can swap it to e.g. WBNB and back to BNB (costs 0.08… €) but every other action like sending to another wallet or binance on the same network does work.
The app always tells me “insufficient funds” without guessing costs.
I thought on bsc you pay with BNB? what the heck am I am doing wrong? My money is trapped :’-(