I mean, “proto-” can be applied to just about any genre as a concept. It’s just people that were making music with at least some similarity before the genre really became a genre. Often they are very close to what would come, but not quite there, hense why they are proto, and not just directly of the genre. They’re a precursor.
So with shoegaze, it started in the latter 80s, and anyone making music that sounds close to it, but came out before then could potentially be considered proto-shoegaze. Especially if they were a common influence for early bands in the genre