Agreed with Salam and others here; get the best GPU you can buy (or get your hands on) as long as your PSU has enough power (i.e. you have 750W Bronze or better, as 3080/80TI/90 will need over 300W) and save for future improvements.
The GPU can take your computer to great levels, even if you don’t have PCI4 ports.
It might help big time too if you get an NVMe drive for all your games (you will also need a PCIe adapter for it) to be installed on.
Those two upgrades will go lenghts for your performance and of course, can be reused in a new PC when you’re ready for a new MB/RAM and CPU.