If the store of your choice offers FLAC as an option (and I think they all do), you can simply make your own MP3s from the FLAC files. That's one of the biggest advantages of lossless audio. (The improvement in audio quality is actually pretty minimal, for most people.)
You can also keep the FLAC files to convert them to some future format later, or even do something really wild like burn them to a CD or something.
I did that for a while, but all the tools seem to have been unmaintained for the last decade. The command line ones still work, but the GUIs to make them easy still depend on qt3 or other such obsolete things. (streaming servers like jellyfin do this on the fly easy, but other workflows for offline use don't work anymore even though they are still sometimes useful)
Most people weite scripts with said tools which can keep going for a long time. I have a couple laying in my library directory to add replay gain metadata, convert to aac, and backup.
You can also keep the FLAC files to convert them to some future format later, or even do something really wild like burn them to a CD or something.