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Take the following with a huge grain of salt as I’m not in your position regarding injury, just some arthritis. Since your D is OK, I’d think you can get to successfully playing 3 finger chords. By “successfully” I mean good enough to get the majority of the sounds in place. I’m going to say there are two main factors of playing chords: fretting hand holding the correct strings so they sound clear and aren’t dampened, and transitions between chords. The first factor will take time for your muscle memory and strength to develop. You are using muscles that you’ve maybe never used and adaptation takes time–even years to master. Having said that, you can be good enough with 3 string chords and that should be your first goal. Look for 3 chord songs that are slow, use 3 or less string chords and easier transitions. This will help with respect to keeping your interest as you get better at making actual music you like. Pick chords that are easiest for you to hold first like the D. Maybe Em, maybe Am or A… you can make a song with these three… AI will actually give you songs names that use the chords you know in the genre you like. Then it is down to transitions and this is all about slowing down and working on particular transitions.
One more thing, when you get fatigued and you reach that point of diminishing returns and frustration, put it down and come back to it later in the day or the next day. At first, 10 minutes or less might be all you can do… put it down, come back to it later. I feel my muscle memory seems to improve even between sessions as if pathways are being built in my brain and nervous system. Maybe not but sometimes I pick my guitar up after a pause between a few sessions and I’m all the sudden better at some aspects that were a struggle. As far as when to move on… I really think it is important to move on and leave things we haven’t perfected. This really goes against my grain and upbringing but it has helped me a lot here as the next weekly routing gets me out of a frustrating rut sometimes and even though I do something completely different in the next week, I get general improvement that is really obvious. The course will circle back to things you practiced a while before, then you’ll see improvement that will really build confidence, desire and satisfaction. Hope this helps!