Open the .rar file in a hex editor. A standard RAR5 file should start with the hex signature 52 61 72 21 1A 07 01 00 .
Only handle this file inside a secure virtual machine (VM) or a dedicated sandbox. Sigma5 Files.rar
Do you have the file size or any specific error messages when trying to open this archive? Support for rar v5 files? - ExifTool by Phil Harvey Open the