Hi,
I opened a similar topic just 2 days ago, see https://forum.inaturalist.org/t/create-a-natural-hybrids-complex-for-each-genus/84450 . The consensus was (as already mentioned): use the observation field and / or create a project.
I would like to add to what ciafre wrote: the observation field can also be filled with “Natural Hybrid”, which opens a field where you can enter a comment, e. g. the parents or something like “parent 1 x second parent unknown” - or also “parents unknown”.
I also created a project (for the genus Tillandsia) to catch all natural hybrids of a genus - which turned out to be 3 projects: one for all nothotaxa of the species, one for presumed hybrids that are not nothotaxa (where observations can get added to manually) and an umbrella project to combine both. Not sure this was the best way to do it, though.