(For my localized 4+3, I only had Eligard for 6 months (two 3-month injections). The Eligard continued to suppress my testosterone (T) levels for an additional 4 months before T levels began returning to normal.)

Yes, libido takes a hit due to low T; that’s expected. My medical oncologist advised me that though the libido will be gone and the “want to” won’t be there, to “do it” anyway. I was told that it’s a “use it or lose it” scenario, and it’s best to keep the blood flowing down there.
> what is his T down to now? (I’ll bet it’s lower than yours!)
> regarding his bone density - what were his DEXA scan results before starting treatment?

While he’s on hormone therapy and his PSA is being suppressed, having a PSMA PET scan won’t be of much value. At very low PSAs, PSMA will miss most everything.
> what were his PSMA PET scan results pre-treatment?

Regarding his lack of energy, what was his T level before starting hormone therapy?
> as for his T returning, how old is he and how many years is the ADT planned for? (And he’s on Zytiga as well?) The older he is affects T returning to pre-ADT levels, and the longer he’s on ADT affects T returning to pre-ADT levels.
> for as long as he’s on ADT and his T levels are being suppressed, he will feel this way. (I often jokingly refer to ADT as Kryptonite!) If that very vigorous resistance-training regimen wasn’t in full swing pre-ADT, I’ve read that it’s very difficult to start exercise later, trying to overcome the fatigue and lack of energy.

The number of years he’ll be on hormone therapy depends on his diagnosis (PSA, Gleason, PSMA PET results, other risk factors, etc.) Depending on the outcome of his treatments, there sometimes can be “ADT vacations.” You’ll have to ask his oncologist.
> can your husband be on Orgovyx rather than the ADT injections?

Yes, ADT is usually used for Gleason 7(4+3) and above; it improves outcomes. ADT + ARPI (like Zytiga) often improves outcomes even more.

For now, he’ll have to keep pressing forward, making incremental changes to improve his quality of life. In time he’ll get there.