A friend has a ryzen 5 3400g. can that be run in crossfire. I know when they started the combo cpu/gpu's they had a list for cards that would work with them for crossfire.
Honestly there are very few games that properly support crossfire anymore. It is discontinued after DX11. DX12 supports multi gpu if the game developer chooses to build support into the game. So far there are only a handful of games that support it.
You are far better off to buy a single card solution that meets your needs. Even in crossfires's hay day, it was problematic at best. A few games would work with it, but more games had issues because of having it enabled.
The best crossfire setups were always the ones where you have to identical cards. With an integrated gpu that is not going to happen.