Hmm, I don't have that frequency. I only have 69 and 70 ;). Most likely, this is also just a quirk of the device.

Are you perhaps confusing the mouse polling rate and the monitor refresh rate? This setting is found in modern mice and is undoubtedly a feature of the device, specifically the mouse; it is only found in USB mice. I have encountered this question several times on the forum, so I suggested adding it to the FAQ, but in any case, I am not insisting on anything :)

For example, this is the setting on my mouse.

Added 3 minutes later

It doesn't work; I've already tried everything... I can't find that save game anywhere, although I'm sure I saved it.

So, you saved the game using quick save, then used quick save in some other game mode and overwrote your old save...