Error importing the data to QGIS
I have tried to download several country boundaries and the resulting geojson.gz file, once imported to QGIS, throws the "is not a valid or recognized data source" error. I have also tried unzipping the file and importing, but the same error occurs.
Here is the permalink for reference: https://osm-boundaries.com/l/93a4c736bd086e136029f5ec4b218130feb55ae0
I'm downloading land only, in EPSG:3857, in case that helps. If I download with water boundaries, however, it works perfectly fine. Weird.
This was new to me, but I found a solution for you. I am not sure if this is only an issue with newer QGIS since I haven't seen it before, it if it's due to some library it's depending on. But I could reproduce it, and I could also find a good workaround.
Assuming you are using Linux you can do any of these:
or
Note that `=0` is unrestricted memory usage. You might want to try with an actual value if you are afraid of going OOM. I went with zero.
If you are running Windows I am sorry to say that we don't know how to help with that. But at least you have a hint then.