Best XT pads for weak hand strength
I can't offer brand and product suggestions but I will say that you could opt for organic pads over sintered for better initial bite. That may compensate for the reduced strength. There's a decent writeup on Pinkbike which coveres the differences between the 2 types of pad.

If you're going to be riding in wet and muddy conditions though, it may be best to swap out for some sintered pads for that ride. Can you get someone you trust to help bed your brakes in? On new and freshly cleaned rotors it makes a huge difference to how much braking force is needed.

Can you brake using a single finger? That should allow you to keep most fingers on the grip for better confidence. My levers are adjusted so the hook at the end of the lever is in line with my index finger.

Although it's a rear brake you can increase your rotor size, possibly by 2 steps if you're running standard 160mm discs. That should give you an increased mechanical advantage. I recently increased my front rotor to 180mm using a postmount adapter. It's a simple job.

The other extreme would be to use one lever to operate both brakes. I've seen a junction box for brakes hoses recently that will allow such a thing. The downside is that you'd probably also need a lever with a larger volume. I think Hope do something that should do the trick.

Lastly, I'm sure you're doing you physio but keep at it. I smashed my scaphoid and several years on I'm stil paying the price. Keep flexing, stretching and doing your grip exercises. If you don't everything tightens back up again and you have to start over.

Nice to see you're still eager to ride though. Good luck.