For Google Photos and Google Drive I'm using filestash (https://www.filestash.app/) pointing to my SFTP server: I can browse my files like any cloud provider, and it generates thumbnails and smaller-size photos and videos for an "album-like" experience. It also contains a very important feature to me, which is sharing. The one thing I like the most is that everything is driven by the filesystem, there is no secondary database that organizes things differently and needs to be kept in sync with the filesystem

It's 80% there for me, I just think for photos there is a little bit more work to do, so I'm going to investigate static gallery tools

For photos you could use a static gallery generator with any cloud backend you want. For example https://thumbsup.github.io/

It's a young product, and still in beta (free during the betas in exchange for your feedback): https://photostructure.com/faq/why-photostructure/ (I'm the author)