I think it is easier if you can specify the country the butterflies are at. Forums used to be the usual place to hang out, year 2000-2010? Then some switched to FB. I lost touch of technology. some are at Discord ?
Second that. It depends on location (btw, it would help if people mentioned somewhere in their iNat/iNatForum profile at least the continent or hemisphere they are from - if it’s not too much personal info revealed…); for France that would be e.g. insecte.org
I would suggest that as a first step you upload some observations of butterflies to iNaturalist. Of course, there’s no guarantee that other users will supply identifications, but I think iNat has a decent number of people who are knowledgable about lepidoptera. It really helps if you use a field guide, perhaps supplemented by iNat’s computer-vision suggestions, to choose a likely species, genus or family. That way your observation is more likely to find its way to people with the relevant knowledge and interest.
If you find that your observations aren’t attracting many IDs, you can look up which other users have provided most IDs for that family in your area and tag them in the comments along the lines of “@rupertclayton, I wonder if you have thoughts on an ID for this butterfly?” No one is obligated to respond, but polite requests are totally acceptable.
As you start to connect with knowledgable lepidopterists, they may know of other resources and fora that would be helpful for your region, but it seems much of what you’re looking for is exactly what iNat is intended to foster.
Unfortunately, there may not be a lot of experts checking iNat observations in some areas. It’s a lot of work, and if nobody has been checking IDs, the backlog of observations that need to be looked at is likely to be daunting. I used to spend some time looking at observations from outside my own area, but in recent years, the number of local observations has grown to the point where I can barely keep up, and as a result, I’ve neglected those for adjoining provinces/states. As for looking at observations for distant areas, where the fauna is unfamiliar, I definitely don’t have time to do the research required to do a proper job of it.