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Several factors can lead to the "unarc.dll returned an error code 11" error on Windows 11:
A corrupted archive is a leading cause of error 11. Repack websites usually include a .md5 , .sfv , or .sha checksum file.
: Open the Run dialog ( Win + R ), type %TEMP% , and delete everything inside to clear out old "failed" install data.
Restart and try the install again (remember to change this back later!).