Ideally avoid XMPP entirely if you can. If you’re just looking for a decentralized and anonymous messenger, SimpleX Chat should be suitable. Even Element (Matrix) would be better.
Privium pointed out that Pidgin (comes with Tails preconfigured to use OTR) probably isn’t the best option. To expand on what AstraKitten said, Gajim and Dino seem to be better options. Tails has considered replacing Pidgin with Dino and even had documentation on how to install it, but it’s now outdated and it seems the community has preferred Gajim since 2022, but Tails has yet to catch up for whatever reason.
So the TL;DR is that Gajim is probably best, but it’s XMPP so you’ll still suffer from some major privacy and security issues no matter what you choose.
Yes, it seems OTR is largely being deprecated in favour of the more modern OMEMO. If my memory serves correctly, it doesn’t encrypt everything and hasn’t been formally verified, so you’re still much better off picking one of the alternative messengers I suggested in the beginning.