The folks at CRS4 have built a OpenSeadragon viewer for OMERO, see: https://github.com/crs4/ome_seadragon
I don’t know anything about it but there are some folks on this forum who are using it: https://forum.image.sc/t/openslide-with-omero-web-to-render-images-not-renderable-by-bio-formats
Another really cool project is Harvard Med School’s Minerva which also uses OpenSeadragon to quickly render very large highly multiplex images to the browser and stores the tiles on AWS S3. See: https://www.cycif.org/software/minerva
They have the original images in OME-TIFF format on their OMERO server and use custom software to generate the visualization tiles together with a story about their data.