Your problem is that your client has updated to Openssl-3 branch. To make that work you have to modify the openssl.cnf file on your client to allow the legacy option.
See thread
https://community.ipfire.org/t/ovpn-cert-creation-algo/7911
The reason for that is that the android client(s) have built in the legacy option while most of the Linux distributions have left that up to people to adjust for themselves if needed.
The thread above gives more info on what the problem between the openssl versions is.