Hi I'm new to speedrunning and recently re-downloaded TS2 on my PS5 (used to have a digital copy on PS3 from the PS store, and was able to upgrade it to PS5 for free). I haven't seen anyone compete with PS5 port before, only PS4. Is this allowed?

Yes, the PS5 Version is allowed. It should say that on the main page and also there's a specific rule for the PS4/5 Versions so if took a look you could have probably assumed it was allowed :p