Also a throwaway. I was hit by non-COVID pneumonia back around 2017 and haven't felt the same since.
"Post-viral fatigue syndrome" was a real thing long before COVID. There's heavy overlap with Chronic Fatigue Syndrome, which for many people starts after an infection.
I will warn you: The online forums and communities around post-viral fatigue syndrome and chronic fatigue syndrome are nightmarishly bad. Don't expect to get any real information out of them. They tend to be more about support groups turned vent sessions for people who are frustrated with their condition.
Personally, I've had decent success with a version of graded exercise therapy combined with psychiatric help. Ironically, these two interventions are despised by the online CFS community because people are afraid that seeking therapy or psychiatric help is an admission that their symptoms are purely psychological. It's not, and any good therapist will understand that.
I've taken the position that my energy levels are diminished, my stress tolerance is reduced, and therefore I need to do everything in my power to minimize stressors in my life. Therapy is perfect for that, so use it to your advantage.
As for graded exercise therapy: Pick a couple basic activities that are easily quantified. Something like walking a specific number of miles, doing a specific number of pushups, or other basic, repeatable tasks. Start an exercise routine with a very low number. Maybe 0.2 miles of walking, or doing 3 pushups in a day if you're really bad. Track your progress and slowly increase the amount over time, backing off immediately when you feel like you've over-exerted yourself. Keep your expectations realistic and resist the temptation to jump ahead of schedule if you're feeling particularly good.
Finally, stay out of the online CFS / post-viral fatigue / chronic illness forums. They're nightmarishly cynical. The good posters have all left, leaving what feels like the "suffering olympics" as people compete to one-up each other on the severity of their illness. It doesn't help, so don't go there.