Hi, there is a bit of discussion about Gerber MTBs in a German forum
and two interesting bikes have been shown
https://www.mtb-news.de/forum/t/der-was-ist-das-fuer-ein-classic-teil-thread.566131/post-16574220https://www.mtb-news.de/forum/t/der-was-ist-das-fuer-ein-classic-teil-thread.566131/post-16574901
Let me translate what a Swiss users has shared:
Gerber was a small bike manufacturer in Oftringen, Switzerland. They went out of business in 2014.
There focus was certainly on road racing bikes,
here is a old catalog
but within the bike boom in early ninties, Gerber also sold a number of different MTBs too, sourced from other companies like Funk (see example above) or even a GT look-a-like.
Looking at your bike, I somehow think that it will have an ITA bottom bracket.
Have you seen that one already?
https://www.retrobike.co.uk/threads/early-1990s-gerber-swiss-mtb-with-tange-prestige.329087/
one more link
https://www.ricardo.ch/de/a/mountainbike-gerber-grosser-tange-rahmen-1158536712/this one from classifieds in Switzerland looks in terms of paint job a bit like yours and has Tange Infinity tubes.