Did you consider automating the publishing of new builds by building them on a CI system like on Travis CI, AppVeyor or since recently, on GitHub itself using GitHub Actions? You can even have it automatically publish to itch.io using butler. I'm doing this for the Tiled snapshots and it saves a lot of time, as well as avoiding the need to maintain a local build environment for all systems. I can try to help out if you're interested.
Yes, I've considered it already. However, Travis CI doesn't support building for i686 or ARMv7 architectures (Raspberry Pi), and AppVeyor required to bundle external dependencies (SDL2 and libpng development libraries for Windows) inside the repository, something I don't want to do. I tried to export 64-bit Linux build on Travis with curl to a ftp server I have, but it failed most of the times, it's a documented limitation it has. So I ended up with a Raspberry PI and VM for linux and OSX, each one with a script that pull sources from GitHub, builds and sends the result to my ftp server. It's really just a couple of minutes.
I've checked Tiled repository and took a look to travis.yml and the deploy scripts to butler. They're a great example to follow in case I want to send at least Linux 64 and OSX builds directly to itch. I didn't know about GitHub actions. At this moment I'm more focued in finishing the main documentation of Tilengine, that's the big hole in my project.
Thanks a lot for your kind help, and congratulations for your Tiled editor! It's an outstanding tool and a key piece in Tilengine functionality.