How to upgrade from Mac OS X 10.7.5 to High Sierra

Hello,

I am on a MacBook Pro purchased in 2011 running Mac OS X 10.7.5

I have never updated it because my professional software did not work on higher Mac OS X versions.
Since I no longer need this software, I would like to update my OS.

If I update directly to High Sierra, this message appears: "This update requires MacOS 10.8 or later."

The Apple website indicates that El Capitan is still available for upgrade for MacBook Pro 2011 versions on Lion. However, once I get to the App Store to download El Capitan, I receive the message "We are unable to fulfill your request. An error has occurred in the App Store. Please try again later," followed by "Software update required. To update your payment information, you must install the latest version of macOS on your Mac."

And so I am redirected to this link: https://support.apple.com/fr-fr/HT208104
This link seems to indicate that my App Store (version 1.1.2 (92.10)) has become obsolete, and thus I need to update my OS. Eventually, I find myself back on the High Sierra page.

Thus, I am stuck in a loop: High Sierra -> El Capitan -> obsolete App Store.
It's a bit like the chicken or the egg story.

That's why I am turning to the forum for help.

For your information, I wouldn't mind paying for Mountain Lion (10.8), but it still needs to be accessible through my "obsolete" App Store and the download needs to work. Unless we can find a free version?

Just so you know, here is my exact configuration:
MacOS X Version 10.7.5
Model Name: MacBook Pro
Model Identifier: MacBookPro8,1
Processor Name: Intel Core i7
Processor Speed: 2.8 GHz
Number of Processors: 1
Total Number of Cores: 2
Level 2 Cache (per core): 256 KB
Level 3 Cache: 4 MB
Memory: 4 GB 1333 MHz DDR3
Boot ROM Version: MBP81.0047.B27
SMC Version (system): 1.68f99
System Serial Number: C2VGKENEDV14

Thank you very much for your help.