I think I understand what’s happened here. You’ve probably clicked on Install Webmin in your VPS control panel is that correct?
The right way to do it is to install your chosen operating system in the VPS panel and then SSH in and install it from terminal. There’s an excellent tutorial here, although he uses ubuntu you may need to find a slightly different one for RHEL (you’re using AlamaLinux) unless you’re happy to use uBuntu instead (which is probably not what you want because AlamaLinux will have a longer LTS life).
Truer words were never said. I’ve actually my own tutorial ready to publish on Flarum’s forum I’m just waiting for Stripe to set up a couple of things for me. I have a long detailed guide explaining how to set up email properly (see mail-tester result) there’s a previous topic with the wrong information lol. The guide is written from POV of running a forum, so full SPF+DKIM+DMARC authentication and SRS for email forwarding (e.g. admin@forum.example.com > youremail@outlook.com).
No it isn’t, what about installing the proper PHP version and then giving it the proper configuration? PHP’s dumb default max upload size is 2MB which is useless for most CMS’s like Wordpress which need to fetch larger files. You should also set up the DNS settings in your DNS zone manager (at minimum an A record pointing to the IP address) before creating the virtual server because that way it will automatically fetch a Let’s Encrypt SSL cert for you. You need to create your DH PEM file as well. Also what the youtuber is doing is dumb - they’re registering a domain at NameCheap and managing the DNS records with Contabo. Just use ONE service for both of those tasks - Namesilo is literally perfect for that. No need to wait for DNS records to propagate since the domain is already setup to use their name servers for you by default - and if you do have your own name server (or your host lets you use theirs) then you can still plug yourself into that any time.
Firefox with uBO you’re my type of guy! 
The only issue with yours is that it gets outdated very quickly. Phil’s guide is kept more up-to-date, but it’s certainly not an exhaustive tutorial either. It’s really more of a guide that’s helpful in understanding the set-up process, but you’ll still want to do things your own way.
Since you’re self-hosting Discourse you should make a tutorial for that sometime and include the resource usage/requirements. That’d be a great resource for your clients, and you could put it in the Virtualmin docs. Speaking of which:
Flarum can do it. Also the WYSIWYG / Rich Text Editor is way better than Discourse’s editor as well. The only things I feel are missing from it at the moment are: 1. having the title and forum in the heading (I’ve got a bit of JS that does this for me), 2. The default theme needs some gentle enhancement, and 3. separating private discussion better from the regular discussions. I disagree with Discourse’s claim that you need to use an external SMTP relay service, that’s a bold claim to make for a piece of software that only generates transactional emails and you only need them going out and not in. For a professional forum it may be advisable, but otherwise it’s unnecessary if you put in the work to set up the SMTP relay properly on the VPS.