I'm having the same issue. I was able to successfully import geoJSON files in an earlier version (3.xx) but not in the last two versions I've tried, including latest (3.70.15). Still get same error message trying to import. Also failed to import geopackage (gpkg) and geodatabase (gdb) files.
Have also tried import via file browser and also dropbox with no success.
Have also tried import via file browser and also dropbox with no success.