I have the same problem:
Catalina installion stucked due insufficent space. Restart with mojave is not possible becaause i can't select any startup volume. if I do a restart anyway, it tries to install Catalina again and stops immediately with the message "no enough disk space".
Tried recovery mode, disk repair (no errors found). Nothing helped.
No TimeMachine backup available.
Tried also to reinstall mojave via recovery mode. Did not work either due "not enough space".
Model: MacbookPro Mid 2017, 128 GB HD
What can I do?
Macintosh HD say it is almost full - with 100GB of data, but this can't be true. The HD is max 30GB full of space
Is there a way to delete (maybe some cache/ temp) files on the macintosh HD - maybe via terminal in recovery mode?
thanks!
Tino