this is , of course, very difficult to determine.
Apparently Instant coffe and normal coffe MAY have the same acidity
https://theoldcoffeepot.com/is-insta...e-less-acidic/
however there is enormous variation and of course what works under certain conditions may be completely not apt to do the job in another.
I have heard on several videos that people prefer the cheapest possible brand of instant coffe, so the first time I used good instant ( and it worked) while the second time I used Cheap instant ( and it didn’t).