If you are having an error specifically with part11.rar , it is likely a "Checksum Error" or "Corrupt Volume." This usually means that specific file didn't download correctly. Most repacks include a .sfv file or a "Verify BIN files" tool to check which part is broken.
Because this relates to files downloaded from a third-party repack site rather than an official distributor, Understanding Multi-Part Archives The Sims 4 -- fitgirl-repacks.site --.part11.rar
You only need to right-click on Part 01 and select "Extract Here" (using software like WinRAR or 7-Zip). The software will automatically pull data from part11.rar and all other pieces to recreate the full installer. Technical & Security Risks If you are having an error specifically with part11