Some additional info:
Paid plan:
Discourse pricing plans
Self hosting:
How Do I Install Discourse?
Third option - self-supported community install
Another option since Discourse is open source (GitHub) and free is to pay a third party to do the site install and regular upgrades. There are down sides to this and the only knowledge I have of this is reading some of the Discourse forum post, e.g. Hosting options (Discourse hosting vs. 3rd party hosting). IIRC there are more 3rd party support providers than just the two in the links noted in this option.
My reply is not an endorsement of any specific one of these options but just something to help those in needing more information. Also while I don’t mind doing the odd admin chores for this site, if this site is self hosted please don’t take that to mean I would be willing to extend the help to doing the install, upgrades and restarts. I am not opposed to assisting others with that but my server admin skills are decades old.
EDIT
For those who are also thinking this might work on a Raspberry Pi 4 it will not but maybe Raspberry Pi 5 when it arrives in a few years.