Downgrading back to Lion?

Can your present computer run Lion?

macOS Sierra: Revert to a previous macOS version

https://support.apple.com/kb/PH25593

I can't find a similar document for High Sierra but I presume the method is the same.

Without a Time Machine backup it is only possible if you have saved a cloned backup using another utility or if you have installer files from an earlier system version (you do) and can selectively update to the desired version.

The Lion in your AppStore under Purchased may not work because the certificate is too old and Lion is no longer offered in the AppStore. You can use Internet Recovery to wipe the hard drive and install the original OS your Mac shipped with. You can upgrade from there if necessary.

How to reinstall macOS - Apple Support

Yes, same process. Back up first just in case.

Why would you want to go back to Lion, perhaps the the worst OS X version ever?

Why in the world would you go backwards. Lion is ancient history.

I suggest you use the program created by Etresoft, a frequent contributor. It will provide a snapshot of your system which we can analyze to possibly determine the cause of your problem. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information