A new release 1.0.136 was created a few hours ago and it is available in the PlayStore already.
Not that I haven’t mentioned this a few times already, but we have WebDAV tests. They pass. I use Joplin on Android with Nextcloud, but I also have a WebDAV endpoint for testing (Apache httpd dav module). It works and it has been working.
So whatever error you are hitting has nothing to do with Joplin, but either with your Android OS (which version are you using?) or the SSL/TLS config on the server.
Unsupported protocol means that the client cannot establish a proper connection. Joplin uses the OS’s layer for that. So it’s either the client OS or the server that provides or requests a protocol (cipher, TLS version, HMAC, …) which is not available (on one or the other).
I’m truly sorry, but these errors cannot be fixed in Joplin.