If I’m reading the “Lifetime concurrent users on Steam” chart on https://steamdb.info/app/753/graphs/ correctly, it’s a slight increase: today 28.0M, 6mo ago 27.9M, 1y ago 25.2M
Jup, Covid caused it to jump from 19 million pre-pandemic to 24 million on april 2020.
But since then, the numbers increased until march 2022, where it peaked at 29 million and, after a short decline by a million until may 2022, currently stays at 28 million.
Notice that if you look at the all-time stats, the decline in the summer happens every year, so it probably doesn't have anything to do with covid.