From QGIS, I loaded Google Satellite from xyz tile layer, and on top of that, I took points from Google Earth to KML and sprayed them.
However, Google Satellite (EPSG:4326) and Google Earth (EPSG:3857) KML coordinate systems do not match each other, and the location is almost accurate.
To match the coordinate system,
Google Earth data was converted from QGIS to coordinate system and changed to EPSG4326, but the location was completely wrong.
Why is the coordinate system wrong?
Best Answer
When adding a Google satellite tile layer to QGIS, it will be projected using EPSG:3857 (also known as web Mercator). This is how these tile layers are displayed.
When creating points / lines in Google Earth and exporting as KML, the points are stored in the KML file using WGS 84 longitude/latitude, also known as EPSG:4326.
When you first added the tile layer to QGIS, that caused QGIS to set its map to display in EPSG:3857. But in GIS software, all layers shown on a map will be displayed in the same coordinate system. Therefore, when you next added the KML points, QGIS will have reprojected those points to EPSG:3857 for display purposes, despite them being stored in EPSG:4326.
If you "changed" the coordinate system of the tile layer by opening it's properties in QGIS and changing the "assigned coordinate reference system" dropdown on the source tab, that will not have changed the data coming from the tile service but may have caused QGIS to misinterpret the locations associated with each tile. That would cause the tile layer and the KML points to be misaligned in the map display.
These coordinate systems are well described here: https://gis.stackexchange.com/a/48952/110158