Ah, ok, got it!
A lockfile doesn’t need much space - if you can identify some snapshots you want to remove, you’ll most likely gain enought free space if you manually remove them from the repository.
I don’t know, but maybe forget --no-lock --dry-run works and enables you to identify what to remove?? Or you use the snapshots command to manually identify what you want to delete.
Another possibility is to use rustic which works without locks. But note that the equivalent to --unsafe-recover-no-free-space (called --early-delete-index in rustic) is only available if you manually build it using the main branch of rustic_core. A next version including this will be available in a couple of days…