Backlog milestone to my understanding is because on trac you couldn't have no milestone assigned. So no milestone and backlog are defacto the same. Personally I prefer no milestone to backlog, tho looks a bit awkward if there are only a few with no milestone. Anyway I treat them the same.
The phab diff says changes planned, so I assume nothing was fixed. If it's still an issue please create a ticket on gitea and feel free to assign me, so I can look into it once I have time.
Would be nice if you actually copied the error message as text (the image doesn't load for me) so a blind guess is you use SetProgress instead of yield.
Probably another instance of https://gitea.wildfiregames.com/0ad/0ad/issues/8757, so reporting it to the fedora bug tracker would be the best course of action as we can't do anything about that one on our side.
Angen and Freagarach, the last two to work seriously on it, both talked about rewriting in the past more than once.
Difficulty levels are almost different bots. Petra isn't a bad bot at all, it just doesn't cover all players. If you change Petra you almost certainly just cater to a different crowd instead.
Well you could make a more friendly one and a more hostile one, then there would be three bots. A bot that better scales with difficulty settings might be another path.
Petra has design limitations, you better create a new one with Petra as a guide only. Writing bots isn't easy but if you want to give it a try and it's fruitful then a lot of value can be added to 0ad.
Petra is in maintenance mode, unlikely to get new features or at least not anytime soon.
A bot can be created as a mod, such a bot could be bundled with the main game alongside Petra if it is mature.
Keep in mind, Petra is generally considered to strong for new players, a newbie friendly bot could help getting more people into the game.