ok thanks for your helpRam 4gb that's your issue right there 8gb would be the minimum requirement, windows is paging like crazy because the ram is full it writes it all out to disk which is about 10x - 100x times slower data transfer speed, depending on the drive you're using. That is a major performance bottleneck.
The cpu temps are probably ok but you should check them in ryzen master anyway I expect it would be something approaching 70c under load, which is normal. You could run the cpu cooler with a better cooler if you wanted to, but it is not necessarily thermally throttling with the amd cooler. Depends what your boost clock might be, could be revving up and slowing down all the time.
If you are using a hdd rather than an ssd windows paging is even slower because a hdd is 10x slower than an ssd which is another major bottleneck.
If you buy another identical dimm it may or may not be compatible with your existing 4gb dimm. Memory is usually sold in kits, dimms bought individually are not guaranteed to work together. They may or may not, that's your chance to take, but a new kit of 2x4gb for 8gb or 2x8 for 16gb is the only way to get the manufacturer guarantee they will work together.
Dunno if you know if the memory xmp profile is enabled, or what the speed rating of the dimm is, you'd need the make model and part number to look that up, doesn't matter if you buy a new kit then start with the qvl for the board as a reference for finding compatible memory.
4gb ram: absolutely a bottleneck. hdd instead of ssd? Might be another one. Cpu thermally throttling, possibly another one.
ps. PSU uknown possible dodgy low quality unit that might potentially malfunction hazardously somehow and at least cease normal operation.