Just to check, why don't you try pulling that USB card and make sure the capture card still doesn't work.
Page 21 of your
motherboard manual states
and page 22 has some sort of diagram explaining what slots are shared and in what conditions, though I can't decipher it.
Some of us have to dial our brains back in time quite a bit, but to me it makes sense to rule out an IRQ conflict before buying new hardware.
Anyway, I guess I'll throw my hat into the ring for new hardware advice 11th Gen
https://pcpartpicker.com/list/H2vZNc or 12th Gen
https://pcpartpicker.com/list/3sFcLs $342 for either somehow the price ended up about a quarter difference. You could also call thermalright to see if they offer mounting hardware for your existing cooler and save a few bucks.
EDIT: I completely missed your question about CPUs OC. Basically manually overclocking a CPU for daily use is a thing of the past. Sure some do it and there's nothing wrong with it, but the benefit vs effort makes it more of a hobby / fun value than a significant cost saving endeavor. CPUs basically automatically adjust frequency within set parameters such that it could be said to be automatically overclocking itself, by default. There are of course lots of minutia and variance between generations, but the gist of it is that you can plug it in and expect that for workloads that rely on speed a single or two cores will boost up to that number listed as "up to" while for more heavy multi-threaded workloads the CPU will function at a power and thermal limit which is pre-defined and will boost well above the base clock but not all the way to the "up to" spec. The other important thing is the memory speed, which is enabled by setting XMP. The difference between 3200, 3600 or even 4000 is trivial for most uses, but the difference between the JDEC spec (plug and play default) and enabling the XMP profile saved to the memory chip (which only takes a few minutes in the BIOS, if that) is notable.
In summary, I guess in the past they were "built to be overclocked" in that every CPU for a set model had to be able to perform the same, so someone could come in and exploit the overhead in manufacturing by overclocking in the past. Now, for the most part, CPUs are able to exploit that overhead on their own which is why clocks are advertised as base and boost or up-to specs.