The expert opinion is that the level of exercise you should be doing is dependent on how long you have been injured for and what your level of activity and fitness level were like previously. The key is to progress it sensibly.
Couch to 5K, which is the NHS’s running protocol, is excellent for someone getting back into running who may have been out for a while. Remember, regression is normal.
Returning to fitness after injury is rarely linear, so be attentive to signals in your body that tell you you’re doing too much. Generally speaking, muscle soreness that passes is fine, but pain is not.