Hey girl - I know this is REALLY tough for you on SO many levels.
For the physical stuff - can you lift free weights for your upper body and do simple crunches (only 1-2 inches of shoulders off the ground) and airplanes for your core? I know it's not the same as the endorphins from aerobic workouts but it can help.
Music also helps with endorphins, can you put together (or find) an upbeat playlist?
As for your friends - I know, it's hard, we're all so worn out and reclusive right now. But there must be online groups somewhere for others isolated at home during this pandemic? Do you have any friends who have also been vaccinated that you could invite over?