Hi Laura!
I've talked a BUNCH about this in my stories and occasionally on posts, but in cases with long covid and CFS, there are often myriad factors at play.
Some of the big ones that we can lovingly step in to support and heal (that are addressable through both nervous system work and lifestyle/diet/light/movement) are working to restore mitochondrial function (using light, movement, minerals like magnesium & selenium, and B-vitamins, especially thiamine, to support ATP production, balancing methylation, correcting nutritional deficiencies, stabilizing mast cells and helping to not only reduce histamine buildup, but to also support its clearance (proper methylation, herbal anti-histamines, vitamin C, quercetin), calming the cell danger response (with targeted brain work to limit the fight/flight response and supplements as needed), balancing blood sugar (to stabilize hormones and keep stress hormones within range) supporting 2-3 bowel movement a day (to keep endotoxin low and therefore support proper mitochondrial & immune function while keeping systemic inflammation minimized), lymph work (to help clear toxins and keep detox pathways open as the body clears things), getting appropriate light exposure to support energy production and circadian rhythms...
I could go on, but those are some of the key pillars I like to start with for anyone dealing chronic symptoms of fatigue.
There's a lot to look at and I see the most improvement when I work with someone to address restoring energy and function from all angles. I know it can feel overwhelming to think about all the moving parts, but once certain habits and tricks are put into place, most people find that they're feeling so much better and far less fatigued that it's worth all the little tweaks and shifts!