So you’ve been using the add-on for 7 days and it was working as expected. The notification you mention is a one-time, dismissible message that can also be permanently disabled in a single click.
Its only purpose is to inform users that they can support the project if they wish. This is entirely optional. The add-on remains fully functional regardless of whether a user decides to contribute or not—no features are restricted.
Even if you choose not to contribute, it’s hard to see how a one-time notification could significantly impact the overall experience.
Given this, a 1-star rating seems disproportionate and unfair.

This is because you've downloaded the "main" branch. You need to download from the release page here : "https://github.com/YouG-o/YouTube-No-Translation/releases/tag/v2.23.0" in the "Assets" section you can find the Firefox zip.

EDIT : v2.23.0 is available on Mozilla. If you installed it via Github, I highly recommend you to re-install it from here, to get automatic updates.

Would be a bit long to explain here, sorry.
Just google "How to install unsigned add-ons on Firefox".

Edit : v2.23.0 is finally available here.