maybe this could be a solution for you.
Edit /etc/httpd/conf.d/nextcloud to put nextcloud to webroot, for making life of ngrok easier:
#Alias /nextcloud "/usr/share/nextcloud/"
Alias / "/usr/share/nextcloud/"
Add ngrok domains to the trusted domains in nextcloud, be careful as this allows all ngrok domains. If you have an own ngrok domain allow only yours.
0 => 'localhost',
1 => 'server.cmb.local',
2 => '192.168.1.11',
3 => 'cloud.cmb.local',
4 => '*.ngrok.io',
Then start ngrok
./ngrok http 80
and browse to your ngrox URL like https://RANDOM.ngrok.io
This is just a workaround, I don't know if these changes will survive an update.
Some webapps will stop working with this workaround, like ocsreports, dl-transmission, webmail, phpmyadmin...and maybe more.