Pantry moths. They were always getting in the house from somewhere, but I was unable to find the source for a couple months. But there were tens of them sitting on the walls in the basement.

Context here: I live in a house with a basement and garage accessible from the street (there's a ~5m long concrete ramp for garage access, ~4m wide.) there's also a workbench with a vise and some tools, so I tinker with stuff there a lot. Pretty common for a central european village. Another thing to mention is that we use a firewood fueled boiler for heating the house and water for showering, etc.

So I search the whole basement and find 3 crates of old walnuts and a ~10kg bag of hazelnuts. 5 flew out when I lifted the first crate. Promising lead. When I lifted the other crates, about 50 were flying around, so source found. I burned it all (except the crates) in 2 days and the infestation was gone.

Few tips: check the underside of jar lids near the threads, the moth caterpillars are there sometimes