Support for Internet Explorer ends on June 15, 2022.
Therefore, there will be more opportunities to use Microsoft Edge's Internet Explorer mode.
This page will explain in detail, with images, what to do when you open a page in Microsoft Edge's Internet Explorer mode and see "Internet Explorer is not found, you need to reinstall or re-enable Internet Explorer." with images and detailed explanations of what to do if you receive the message Internet Explorer is not found.
This site is run by Japanese.
All the procedures explained on this site are compatible with Japanese Windows OS.
My translation and operational mistakes may have an unexpected negative effect on your computer.
Please use the site at your own risk.
I try to explain and translate as carefully as possible, but if there are any mistakes in my explanation or translation, please let me know in the comments.

I recommend that you complete the Windows update and bring it up to date before implementing the procedures described here.
How to add Internet Explorer mode to Windows.
When you open a page in Microsoft Edge's Internet Explorer mode and see "Internet Explorer not found, you need to reinstall or re-enable Internet Explorer." then you need to add Internet Explorer mode to your Windows features.

Click on the "Windows button" on the taskbar (or press the Start button on the keyboard).
After clicking on the "Windows button," the menu will expand upward.
Click on the gear icon "Settings" in that expanded menu.

Once you click on that "Settings," a window labeled "System" will open.
Click on "Applications" in the menu on the left.

Once you click on that "Apps" link, you will be taken to a page labeled "Apps".
Click on "Optional Features" in that section.

Once you click on that "Optional Features", you will be taken to a page labeled "Apps > Optional Features".
In that page, click on "Show Features" which appears to the right of "Add Optional Feature".

After clicking on that "Show Features", you will see a list of features that can be added as optional features.
Find "Internet Explorer Mode" in that list and check it.
After checking the box, click "Next".

After clicking "Next" earlier, you will be taken to a screen where you can click the "Install" button.
Click "Install.

After clicking "Install" earlier, the computer will return to the "Apps > Optional Features" screen and the installation will begin.
This installation takes only a minute or two.

When the installation is finished, a message will appear asking you to restart your computer.
Please restart Windows.
It will take about 2-3 minutes to reboot Windows for additional functionality.

If you open the page in Microsoft Edge Internet Explorer mode after restarting, the page opens normally in IE mode.
How to add Internet Explorer mode to Windows from the command prompt.
To enable Internet Explorer mode from the command prompt, the command prompt must be started as administrator.

After launching the command prompt as administrator, type the following command and press enter.
dism /online /Enable-Feature /FeatureName:Internet-Explorer-Optional-amd64

If the command is entered correctly and the enter key is pressed, the message "Operation completed successfully." will be displayed.
Although not shown on the screen, you must restart Windows after adding Internet Explorer mode to Windows from the command prompt.
If you open the page in Microsoft Edge Internet Explorer mode after restarting, the page opens normally in IE mode.