You can call me a madman for this but I found the Mewtwo Raid among the 6*/7* to be the most 'doable' with the assumption that at
least one Mew (preferably Bug Tera Type) is present. Since everyone gets Mew, this isn't an excuse for any non-NPC players to not use it tbh. I found that as long I could break the barrier and also debuff Mewtwo (I basically spammed Snarl), my chances to beat Mewtwo were really favorable after 1/2 HP. I also got lucky with dealing damage when Mewtwo would use Rest so it never actually got to heal
Was able to beat it 4 times (out of 8), all with me having a Steel Tera Mew (only had ~20 Bug Tera Crystals so I couldn't change types). 1 Win was with 4 Mews (3 Bug, 1 Steel) and the other 3 Wins had 1 Bug Mew + Steel Mew (me) + 2 NPCs (Paldean Tauros, Gallade, Clefable). The 4 losses was from. All of them had our Mews fainting several times but we still had more than enough to win. I basically spammed Snarl to keep Mewtwo from doing a lot of damage while the other (Bug) Mew set up with Swords Dance + Leech Life to finish off Mewtwo
I found in the past year of doing 6* and 7* raids that the raid pokemon would often attack 3-4 times in a row (I had as much as 8) before I even got make an action (eerily similar to PLA) and I always struggled with these types of raids since I and other people would get oneshotted if the raid pokemon did a set-up move like Swords Dance/Dragon Dance/Bulk Up/etc. The lagging and missing animations in normal 6*/7* was really anooying as well (like having the countdown go from half to '___released its gathered energy' in a span of 10 seconds). All of the other 7* star raids admittedly took me 20+ attempts to beat once (Delphox, Chesnaught, etc)
Having Mewtwo attacking only once per turn (after the initial Calm Mind + Tera Barrier) before/after I made a move was honestly very refreshing and much more manageable since Mew's good enough to tank Ice Beam. I also realllly appreciated the countdown timer being much more generous with Mewtwo since at least for it me it stopped moving much at all once i broke the barrier
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early start for me on the DLC 😅
gonna be doing the same strat that I did for SV's story mode and complete the Kitakami Pokedex/reach all of the areas before I complete the story w/ Ogerpon
also I hope its not only me but I've been having legit troubles getting into any Sinistcha raids (5* or 6*), they never seem to load and I always get the 'you weren't able to join' notice >:(