Error 99999 All raster processes fail in ArcGIS

I’m using ArcMap 10.8.1 and wanted to e.g. do a slope calculation on a Digital Elevation Model.

Now I´m getting Error 999999 which usually refers to a bug or some unexpected error. First I thought it´s the one DEM but no other DEM raster works. So the program has a problem here. Hillshade also doesn´t work, gives Error 010067, Aspect Error 99999, Contour lines work.
Raster calculator gives the error "format GRID" whatever that means now.

It seems like all map algebra processes are buggy for me.

Should I reinstall or do something else?

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I´ve reinstalled ArcGIS on this computer: No Changes.
I´ve installed in on a second computer: No Changes.

The Elevation models used mainly for testing for the error are:

srtm_lev_bnd21.tif
Cell size: 0,00029550817, 0,00029550817
1.66 GB
32 bit
GCS_WGS_1984

SRTM_30.tif
Cell size: 30,30151988, 30,30151987
1.4 GB
16bit
WGS_1984_UTM_Zone_36N

jor_utm.img
Cell size: 29,23080851, 29,23080851
98.91MB
16bit
WGS_1984_UTM_Zone_36N

dem_l8_5x5_high_clip.img
Cell size: 0,5, 0,5
3.33 GB
32 bit
UTM_Zone_36N