Reconditioning your body after years of inactivity - ME/CFS Long Covid

I developed ME/CFS symptoms after a covid infection.

Long story short I wound up barely able to get out of bed from late 2024 to jan 2026. I was literally bed bound for a big part of 2025.

I am now recovering, gaining some energy back where as before I could barely type. My recovery is quite rapid over the last 3 months in terms of energy and improvement in symptoms.

Only issue is, I fear my legs have become deconditioned, it seems. I haven't done any serious exercise since 2023, and for much of 2024 I was only walking 4-5k steps at most per day, reducing to being housebound from september 2024 onwards.

If I even do a few flights of stairs (only started doing stairs and uphill last few weeks) my knee aches quite badly, and I can't do more than 5k steps per day. Energy is increasing well but parts of my body lag behind. I was making great progress until I hit this wall. I was able to walk 7-8k steps until I go the aches starting and had to cut back.

TL;DR - After a long period of inactivity cause by serious ME/CFS (long covid related), did any of you suffer with deconditioning issues and problems such as soreness, (patellofemoral pain syndrome) in knees or other issues etc? What did you do?

What did you do to recondition your body? I feel fitter but still weak in the legs. I've only been walking significant distances for 3 months, and feel like I made good progress.

I have a physiotherapist booked. I worried I'll never be able to hike or work out again.

This is not primarily about fatigue, but more your journey to reconditioning your body while recovering from CFS?