Hi, i have the same problem since 2020.
I live in Poland, in an old apartment from the 80s.
Till 2020 it was a really smooth gaming experience, then i bought a new PC and... here i am.
Frametime spikes/Stuttering all over the place, even in low-end games like cs go, rocket league, battlefield 1, half life 2, skyrim... it's crazy
Literally i've tried everything (rgb off, all windows settings, bios tweaks, new drivers, old drivers, underclocking, overclocking, swapping parts and much much more)
Also it happens on my ps5 and Iphone 12, and sometimes im feeling that my tv is "infected" too (how? hbo/netflix menu has awful frame-skips) so definitely there is nothing wrong with my pc.
Unfortunately i have no clue how to fix that.
Begging for help, any ideas? :/