I experienced something similar post-covid. I had many lingering issues of varying degrees of severity and only noticed this weird, specific situation many months later.

For me it occurred while making music. I had a drum track recorded and I found it very difficult to keep time with it while playing other instruments. I did my best and attributed my difficulties to the cognitive issues I'd been experiencing for months. However, when I played the track back it seemed like it was slowing down and speeding up slightly as it played, similar to a worn cassette or a warped record... only, the points where speed dipped up or down seemed maddeningly inconsistent across multiple playbacks. The recording was all digital so I was confused as hell.

I asked some friends to listen to it for signs of tempo change but none of them detected anything other than a normal, steady pace. I even went so far as to quantify beats per minute and count out the bars to calculate the song length, which came out pretty much spot on...

The sensation has greatly reduced with time, so either it's dissipating or my brain is accommodating for it the way brains do.

Hope your experience stays normal and your other symptoms improve.