import xarray as xr

# Rhine's basin bounding box
bbox = [50.972204, 46.296530, 5.450796, 11.871059]  # N,S,W,E

ds = xr.open_dataset("glofas_historical.grib", engine="cfgrib")

ds_cropped = ds.sel(
    longitude=slice(bbox[2], bbox[3]), latitude=slice(bbox[0], bbox[1])
)

ds_cropped.to_netcdf("glofas_historical_cropped.nc")

When transforming from lat/lon (source coordinates) to projected LAEA (target coordinates), you need to consider that the number of decimal places of the source coordinates affects the target coordinates precision:

An interval of 0.001 degrees corresponds to about 100 metres in LAEA.

An interval of 0.00001 degrees corresponds to about 1 metre in LAEA.