[deleted] Thank you for your input .
I guess you use default VPN settings set by Proton : "Always-on VPN" and "Block connections without VPN" are both "on" ?
I just installed Proton VPN app on a new profile, activated airplane mode, and I'm waiting for GOS app "Apps" next update. (*) So far apps like Vanadium act exactly like with Mullvad VPN app : they have no clue that connection is down and try to connect until reaching timeout.
(*) Edit : and it's done : problem reproduced with Proton VPN app. "Apps" app triggered the usual error while trying to update while airplane mode was activated and Proton VPN used.
The more I dig this subject, the more I think it's an upstream problem, and that "OS connectivity check" is almost useless when using a VPN... because even if it checks connectivity, the information is not handed down to apps, or maybe overruled by apps' own network detection process (which can be shortened as "If VPN present : internet is UP")