Based on an idea and a request from Tomasz, I suggest :

In gallery it should be possible to specify a thumbnail - or alternatively -  in a checkbox have the possibility to set if   thumbnails should not be updated.

This way it was possible to first have the checkbox unchecked and then the thumbnails was created. Then - when the gallery is at it should be, then check the checkbox, and then you could edit the thumbnails and they would not be overwritten by a new upload.

See this post for further information :  https://helpcenter.websitex5.com/en/post/205510

This would make it possible to use the gallery as a multi-button. You have the thumbnails as buttons/texts, and by clicking them, you would see an image maybe with some text, and then when clicking the image you was directed to a link that is set for the image.

You could achieve much the same with an iframe, and some links that targets the iframe, but this with the gallery, could be made without code - you just have to know how to edit an image ( the thumbnails).