Thanks for mentioning Paddle, I didn't know about it. Seems a good alternative to FastSpring, which I've used for ages.
They basically make the whole tax problem disappear, and you just focus on building the product and helping the customers.
I am a solopreneur, so I don't really have time to manage taxes on my own, and I'm glad that a company takes care of that as a reseller, and I just have to interface with them.
FastSpring is great, I use it but it seems a bit in maintenance mode, meaning that I've not seen a new meaningful feature that's not a simple addition to the things they already offered 5 years ago, and I always asked myself why there is not much competition in this space, as there is a lot of money to be made in this kind of business, or at least this is what seems to me. Paddle is one, maybe you know others?