SO should I just ask the casino what format their bitcoin addresses are in? Do they start with bc1 or 1? will they know
The format of their addresses doesn't matter. Electrum allows you to send coins to any kind of address (segwit or legacy, bc1 or 1) regardless of the wallet type you have.
The problem is that when you are going to withdrawal your coins from the website to your wallet, some of them think addresses starting with bc1 are invalid, so you need to create a legacy one (starting with 1) to receive the coins. But that's just a problem on them. Even if they only support Legacy addresses, you can still send to them from Segwit addresses.
If you are worried about this, you can just create a legacy one as it will work in all websites, or use Segwit until you have any issues, then you create a legacy to receive the coins from the website that doesn't support it.
This was really serious issue with me but today after reading your this post I solve this all and now feeling much better because I was unable to withdraw funds from few sites just because of bc1 but now all clear.