With a thermal imaging camera, you will always find (Unavoidable) thermal bridges at windows... this is even the case with the most expensive passive house windows. A house free of thermal bridges does not exist. The paper strip test can only check whether the seal is in place (= functions) .... how much pressure is applied to the paper is usually not particularly meaningful. Windows can be inspected/maintained/repaired/... by experts, which is usually sufficient. It is even possible, approximating current DIN standards, to precisely determine the airtightness of installed windows through elaborate tests. In the photos in #4, I believe I see windows according to Din... "IV56" that were installed approximately from the late 70s/early 80s to the late 80s/early 90s. "IV56" was a tested system that easily meets today's requirements regarding airtightness if the windows have been/are properly maintained or are still in good condition. Glazing can be replaced so that the windows even (almost) meet the mindset requirement (Uw <1.3) for a new window (Uw approx. 1.3 - 1.5).
