There’s a list of apps with various degrees of support.
You can deviate from it and install other stuff, but in that case you’re mostly on your own, they may or may not work as expected.
I can't recall ever seeing preinstalled yunohost vps's. Only the the images themselves https://yunohost.org/en/images
I have ran the installer command on couple of vps providers including vultr, digital ocean, and hetzner without facing any issues.
You will have to initially secure the vps yourself. Quite a few articles out there how to do this. Then you can use yunohost tools to manage the ports and keep everything updated.
There are quite a few things you can do as there are different levels of hardening you may wish to Please search for it. but dont get scared off. To get you started here are couple of things I've done. Go at your pace.
editing the /etc/ssh/sshd_config file to remove root from accessing via ssh, removing password access & using keys only, change default ssh port
disabling any open ports that are unneeded (use something sshguard or fail2ban
use a firewall
carefully allow sudo to do only the absolute necessry things
be mindful of how you secure wordpress or any other similar apps
and run lynis to check the security at a deeper level ( https://cisofy.com/lynis/ )