it may be an opportunity to look into weight training. You can pick exercises where you can sit or even lie down. Even machines which ordinarily are not on my favorites list are an option at this point in time. You can also look into flexibility and do some stretching as long as it does not involve the injured tendon.
Six week is not such a long time after all but you need to let it heal. If may also be worth talking to a physical therapist to find out what causes this chronic inflammation. The posterior tibialis tendon does not all of a sudden decide to get inflamed. There must be a reason, and I would suspect it has to do with the way you move and walk.
I wish you a speedy recovery.