I tried to install the extension on a new Chrome install and saw that error in the web store too.

The extension likely doesn't use the new Chrome Manifest v3, so support for the extension will be deprecated over the summer when Google stops supporting Manifest v2.

https://developer.chrome.com/docs/ex...te/what-is-mv3

If your Tampermonkey script is just retrieving the script from the Chrome Extensions web store, it'll stop working at that point because Google will likely remove the extension.