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Download the files at: https://www.naturalearthdata.com/downloads/110m-cultural-vectors/110m-admin-0-countries/
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Convert them to GEOJSON with QGIS3.12 (https://www.qgis.org/)
- Keep these keys when converting: ADM0_A3, ISO_A3, ISO_A3_EH. With these, the country can be idetified later.
- Use only 2 or 3 decimal places. This is enough details.