Given how old is the original theme and the absence of an official follow-up or fork, even if you manage to find a working link, I think you can’t rely on this theme. If there isn’t an issue with it currently (I don’t know really), there will eventually.
Plus, but that’s my own experience, bbPress is horrendous and slow.
I’m fairly sure that migrating Flarum to bbPress will be a painful and deterrent experience (I don’t even know if someone actually did such a thing) and that if you need modern software to host a community, Discourse is the number one choice (I have no affiliation with them).
Plus, there is a built-in script to migrate from Flarum to Discourse. See https://github.com/discourse/discourse/blob/main/script/import_scripts/flarum_import.rb
I’ll let you use a web search engine for further information…
I gave it a try 3 years ago. It was working, but a bit incomplete from what I remember.
I didn’t keep it and moreover, I ditched bbPress, I think it is a horrendous forum system, slow and clunky.
I now use Discourse which I have connected to my WordPress with the plugin Wp-Discourse. It has been 3 years and I couldn’t be happier.
Sorry for being a bit off-topic though.
