Where do we go now ?
Excuse my french if my post isn't clear. I'm still learning.
Welcome here to Vanilla's death. It's sad to say as I was using it since 2012 and was even devlopping addons for vanilla (with variable quality one might argues) but as we know today, the last stable pre-compilled released of Vanilla is 2021.009, wich dosen't support PHP 8+ at all.
These concerns are multiple, as Vanilla OSS can't be counted as maintained anymore. Why ? Because all new "releases" on github are not pre-built and and there's no real release in sight. So most forums will have to stick to 2021.009 (or even older releases) wich means no security update, breaches not covered etc. Third-party security is also important but it leads to my next point:
PHP 7.x is on it's way out. Yes, PHP was late to this fast-releases paradigme BUT now they're going fast with security in mind, while implementing breaking changes to also improve performance. On many hosts, you can't really choose wich PHP version you can use (most will limit you to supported PHP versions plus the most recent unsupported one). It may makes a lot of forums down like the "mysql_connect isn't defined" plague we faced when PHP 5.5 was released.
Vanilla was a great forum software but was doomed as an open source software. It seems that some persons in VF, Inc. wanted to ditch the open source version for long, and work on expensive af hosted service only. They were in their right of course, but it can feel kinda deceptive in some ways, for the OSS users. The final nail in the coffin might have been the acquisition who put Vanilla OSS in the bin, for good.
So where do we go, from now ?
I used Vanilla and helped non-profit organisations to migrate from old forum software to Vanilla: now I'm making them using more promising software, with a clearer business model oriented around it's open-source core.
Fortunately for us, many forum and community softwares do exists but a lot don't support migration from Vanilla. As @Linc seems to work on a porter version that can be used to go all steam to Flarum, it isn't all lost. The "Porter" format might be a great way to grant communities portability. Let's keep an eye on it. See post below;
To use it and follow developpement, I might advise you to check out the project website: https://nitroporter.org/
If you want to create a community from scratch, you may want to choose something other than Vanilla. The future of this software seems dark, except if some "community edition" pops up from a volunteer like what happened to the WebsiteBaker CMS.
I'm really sad to see this software dying and would like to help maintain it as a free and open source software but that's beyond my capabilities. Vanilla has a great features set.