therapists/assistants tend to do more lifting in SNF, in pt, hospital settings HH not as much in outpt but you there you may have to a lot of manual work - afterall you want to do things with the pt that they can't do at home so a good therapist will try to do more manual work or at least some - PNF, ROM, etc but also measurements positioning of limbs, muscle manual testing (MMT), tissue mobilization, if indicated of course vs whole session of just exercises while in clinic, also consider amount of documentation mostly electronic these days but some might still have you writing on paper which may aggravate symptoms.
Part of the job application or contract will usually a list of "must be" and you will likely see: must be able to lift up to 30 or sometimes 50 pounds for many facilities/clinics among other things.
Having said that I have worked with therapists in their 60s and they too are fairly fit and they've been able to handle the requirements just fine.
See if you can observe both sides and different therapists different settings and see which one you think might work better for you.
Maybe you can see a certified hand therapist in the meantime and get treatment to manage the pain and learn modification techniques, jt protection, etc.