Can't find High Sierra 10.13.1 in App Store. Need a download link

Back up your data, check your applications for compatibility, and if your Mac model is recent enough, click on High Sierra. This version can upgrade previous OS releases; if you're specifically looking for 10.13.1 instead of High Sierra in general, you'll need to have kept a copy of the installer.

To check the programs, click here and look them up.

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That is because the last FULL VERSION of High Sierra offered by Apple is version 10.13.6. If one finds a version of High Sierra 10.13.1 that is probably only and Update and Not A full Version.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal  operation of the OS and may even Corrupt the OS requiring a Reinstallation