Hello all !
Ventoy is a multi-boot USB creator, which runs perfectly for installing Solus (Budgie, in my case.)
Download it here:
https://www.ventoy.net/en/download.html
I've downloaded the Linux version, so unpack it wherever you want, plug a USB stick in your computer, and run whatever VentoyGUI you need. Once this is done, you can simply drag and drop on your USB stick as much ISOs as the stick is able to get.
Insert the USB stick in the computer you want Solus to be installed (or whatever distro you want), start the computer, and you'll get as many entries as you have ISOs. Simply choose one, and voilà !
Cheers !