I’ve also been trying for a while to get my own certificate to run locally.
unfortunately nothing.
Now it works with nginx proxy manager.
Nginx with docker and forward there via the open port.
But it only works if no other service uses port 80/443
my tip: use an extra raspy for your project.
i installed docker with dietpi and then added the docker images nginx and vaultwarden.
everything in 10 minutes.