When I want to withraw from coinbase it seems I cannot choose network..I wanted to deposit to exchange that offers bep20 and erc20 deposits...anyone familiar withdrawing from coinbase¿?
Coinbase does support multiple networks. The list of networks should show after you write the amount and all. What is it you're trying to withdraw?
But if I had to guess, I would say they probably don't support Binance's smart chain, as only a few exchanges support that. So if the coin only has two networks (BSC and Ethereum's) its probably withdrawing to the default one (Ethereum) but I would imagine that the withdrawal page does mention that.