I checked, Server 11 doesn't do any check, months that I read about the tiniest thing and no one noticed that "detail"
I did some tests to shed more light on the matter. About point #2, Server 11 installs on old HW by design, no question asked. Regarding point #1, I tried to start an installation/in place upgrade starting from LTSB2016 with the following results. Server 11 = OK Win 11 = OK (it complains about the unsupported HW but that's a different matter) Server 2022 = OK, even the 20348.1 ISO which was still named as preview Server 2004 (no GUI) = OK, even the initial 19041.208 ISO Client 1904x (any version) = KO Earlier Client SKUs = KO Server 2019/Server 1809 = KO I don't have any Server 19xx to test ATM Client 1904x WIM placed inside 19041 Server ISO = KO