I had a curious effect after installing Linux Mint 20.1: Darktabe 3.1 produced jpg and tiff files which appeared too dark in pix and nemo. in Darktable and geeqie everything was normal. When I installed Darktable 3.4 the effect was gone, in 3.5.0~git848.05dfc1d48-1 everything appeared fine too. Yesterday I was updated to 3.5.0~git849.e1596a3a4-1 and the effect reappeared.
I am (less) happy now after reinstalling 3.4.0.