once the encryption service is setup correctly, no further action is required
the service will be activated and will check if certificate renewal is necessary
sudo snap services nextcloud
if you have previously disabled that service, you may need to enable it again so that it is active see Managing services
sudo snap enable nextcloud.renew-certs enable the service
sudo snap start nextcloud.renew-certs start the service
sudo snap start --enable nextcloud.renew-certs start and enable service
sudo snap restart nextcloud.renew-certs restart the service
read the docs