It seems supplements work differently for each one of us.
I for instance did try Co-q10 and Acetyl L Carnitine as well as a half tablet of B12 daily and vitamin C, as well as B complex low dose, Vitamin D3 400iu daily (which is quite a low dose but better than you get in an average multi vitamin and mineral.)
I have also tried chelated Magnesium, small doses every two hours.
I think the D3 helped me. I think the B12 helped possibly, though I am not sure. I came off the B12 a week or more ago, and am weighing up any differences at the moment. I have had some fleeting neuropathic pain since stopping it, so am deciding if that is coincidence, or related to stopping the B12.
Otherwise the other supplements made no difference. Yet occasionally I would feel a little boost from 2000mg Vit C if I was crashing.
L Carnitine possibly messed slightly with my sleep (frequent wakenings) So I stopped that for the moment. I hadn't taken it long enough to notice any energy improvements.
I am sure others here will be able to recommend supplements which have helped them.
I haven't noticed much change on mine.
Landscaping is really hard work. If you are mild, you might be okay on some light exercise daily. I know I am okay with that -though on some days I am not and have to admit it.
General maintenance gardening might be easier and not force your body too hard. (pruning trees/lawn work/strimming (weed-whacking) etc
Even I think I could probably cope with that work, doing it part time. But there are days when I couldn't.
But (and I am sure I am older than you, in my late 60s) I have always been used to hard physical work all my life, and right up to the onset of ME/CFS early last year...yet even though fairly mild I think, wouldn't test out doing full or even part-time landscape gardening.
It is so important to not push the body into a crash. We always bounce back.....until we don't any more, and there have been cases of some people who were moderate pushing so hard they became severe. We have a whole new life to live, a whole new set of ways to get used to.
I hope I don't sound negative. I am sure I do....I am sorry.
(later edit)...BUT...a thought came to mind. Management of a team of landscape gardeners/forming a landscaping company etc might be an option? Nobody is asking you to carry so many rocks that way...lol and you can still work creatively?