DDR4-3200 should run just fine on a 9th gen Intel CPU. If your intent is just to buy a new kit (and not to pair it with your existing RAM) then I'd recommend getting either a DDR4-3200 or DDR4-3600 kit, as those seem to be in the sweet spot for value.
Long story short, RAM speed compatibility is largely determined by the quality of the memory controller on the CPU. By 9th gen, Intel CPUs could easily hit DDR4-3200 speeds and most could also handle DDR4-3600, some could even go up to DDR4-4000. This was not the case for AMD CPUs of the time - some Ryzen 2000 series chips struggled to even hit DDR4-3000, let alone higher frequencies.
The optimal RAM speed for each generation of CPUs is mostly determined by the collective wisdom of the PC community - people tried out RAM configurations and shared their results and/or reviewers tested a bunch of RAM kits on a CPU. The officially supported speed on the CPU is almost always going to be lower than the optimal RAM speed, and motherboards will often support ludicrously high speeds that are not actually achievable by most CPUs on the platform.
So if you're not on the pulse of PC hardware, asking here about your setup is a good option.