Yes. On a PCIe 3.0 only system, get the 8GB model or just get something else. The performance difference between PCIe 3.0 & 4.0 can be significant. (In this case, I'd definitely just get something else tbh. Assuming your PSU isn't ****, RX 580 8GB's can be had for peanuts w/ similar perf to a 5500 XT and lower end Ampere & RDNA 2 cards are incoming ASAP).
On a B550 based budget rig though, the RX 5500 XT 4GB can be a pretty good card, assuming the price is right ofc. (If it's not though, buying a 4GB card atm over say a used 8GB RX 580 is pretty freaking stupid as a long term move. 4GB of VRAM is ALREADY not enough for modern titles maxed out at 1080p [hence the perf gains w/ PCIe 4.0]).