So someone already mentioned this, but there is this list I maintain on Codeberg: https://codeberg.org/RayJW/awesome-foss
There is also this website which is pretty neat if you're searching for an alternative for a specific software: https://www.opensourcealternative.to/
Hot take: but I think it makes sense. If anyone would pay for a closed source editor it's mac developers hence it made sense to chose that as your first platform to support, especially considering that they are a small startup. I don't use mac either but I think they made the right choice from a business standpoint when they were still closed source.
Just so you know, libimobiledevice can backup iPhones with their idevicebackup utility. It's CLI only, so maybe not as easy to get into as iTunes but it has worked pretty well for years on my end.