How to disable Vo2max/training status calculation for one bike/power meter?

No solution for it. Btw, how do you know that the emtb's powermeter is low and not the other is high?

it's just an assumption, coz power meter on my road bike, gives very similar results to 2 other road bike power meters I used (on rented bikes)

what kind of pmeters do You have (on ebike or what the bike's type/model and on the road?) just to find out what could be the problem and is there any possibility to get a match between these two pmeters

Turbo Levo gen3  and 4iiii,  I could lower power readings in 4iii power meter, but then all my stats will go down, so I prefer not to.

a left-only 4iiii never will be accurate , if somebody has left-leg dominancy , easily can measure +10% (with 55-45% leg balance), and i have many friends who bought at 1st single-sided powermeter and their pedaling technique went wrong due to they all wanted to get the biggest numbers and they guessed that if they push a little bit harder with left leg the numbers will be bigger (but they forgot that the pace is not increasing in this case... :D ). So dont trust in the 4iiii neither... get an accurate indoor trainer, put both bikes onto that and make dual recordings, and that will give you the answer which is low and which is high. i "know", always the higher number is the "valid" from watt and vo2max, and always the lower number is the "valid" from weight if you have 2 devices with 2 different values... 

as I mentioned, mine 4iiii was compared with 2 other double sided power meters and results were very close., that's why I'd say I trust mine 4iiii more than power meter on my Levo gen3

if those "duals" were Power2Max NGs, then ok, if not, i dont trust in nothing (i have more than 10 years experience as powermeter expert so i have seen a "few" miracles...) but everybody thinks what he wanna think or believe in things. 

back to the original question, no solution

it's enough for me that I have consistent results.

try to write to the specialized (via the levo app support), to implement a power scale menu (as almost all powermeter brands have such a scaling feature in their own app) and if it is ready, You will increase it with the desired value.