So my understanding is that long COVID can reduce mitochondrial ATP production across the board.
The urea cycle, the process by which the body converts the waste product of protein breakdown, ammonia, into urea is highly ATP intensive.
Thus the urea cycle can be damaged without any long term damage to the liver (which is good news)
The bad news is this can lead to relatively mild ( relative to alcohol related liver disease) hepatic encephalopathy.
More good news, this is treatable.
More bad news, doctors are taught that urea cycle disorders are either genetic or as a result of a damaged liver.
Yet more good news, the support the urea cycle needs is available without prescription.
By eating the amino acids that your body expends enormous energy manufacturing, you save it that effort, the idea being that that energy can now be used deploying those amino acids in another ATP intensive activity, converting the ammonia into urea.
Then there are ammonia scavengers which will remove ammonia from your system using methods that don't involve ATP.
If you have the funds and a functional relationship with a physician who knows more about this than you do, the speak with them before ordering a bunch of amino acids and a food preservative.
And yes, the cells that make the amino acid substrates for the urea cycle, hepatocytes, are the same cells that convert the ammonia into urea, so, theoretically, the ATP saved in one intense process can now be deployed in an environment where there is enough substrate to convert the ammonia to urea.
So if you find eating more protein makes you worse, more tired, more irritable, less likely to make memories, or remember old ones (how many doctors understand that difference?), and/or NAD+ precursors make you worse, these are signs that you may, underscore may, have a urea cycle issue.
If you can eat double your usual protein and not worsen your situation it is highly unlikely that this is one of the issues affecting you.
If it is, manage your expectations.
This doesn't fix mitochondrial damage. It does mitigate the damage in one very specific, very necessary, process.
So it ain't a cure, no magic bullet, but possibly the foundation on which you can start to rebuild.
Good luck