Depends on the case and other cards, if any, also installed in PCie slots. For an open air case, for instance, you could put an RX-6900XT in it since there would be no space constraints. But it would be a waste, as the CPU would hold it back in the meaningful gaming for which it's built.
The better question is how much GPU and that depends as much on the gaming resolution you play at.
Most likely a decent 'fit' would be an RX6600XT: probably way more than the CPU can handle at 1080P but once you get the urge to upgrade CPU/MB/Memory it will at least be adequate for a while.
But a more perfect 'fit' would be on the order of RX550 or GTX1030, which will be much more reasonably priced too since they're not really great gaming cards for modern CPU's.