Hello , welcome ! I am another member such as you always looking to get more information about our shared illness. Sure is a lot to learn. Even though I am not a medical professional, nor can we give out medical advice here, may I suggest that you check with your doctors to make sure this is not some other medical issue giving you problems with your legs. Not only do I suffer from the COPD that is causing some edema right now, but I also have Venus Reflux, this is where the valves in the legs do not work properly, thus causing circulation problems too. Something to think about.
In the mean time I did find a could sights about COPD and Leg fatigue for some interesting reading.
https://pubmed.ncbi.nlm.nih.gov/16135172/
https://pubmed.ncbi.nlm.nih.gov/9700144/
https://erj.ersjournals.com/content/33/4/763
Hope you find this helpful in someways.
best to you,