Mobile app does not respect/use installed *client* certificates

I have nextcloud installation that requires client certificates (aka mTLS).

All the apps (!) apart from nextcloud (!) work perfectly fine:

  • Mobile Chrome
  • desktop browsers
  • DavX5

but the official nextcloud application fails: after I fill in “server address”, it says:

SSL initialisation failed

which is not very surprising, because unlike any other application, it has not asked me which client certificate to use.

Is it expected?
Why is the official app is the only app that does not work?..