There’s all the usual stuff like Google Drive, Dropbox, and any of the other multiple cloud storage services out there. You can chuck a certain amount in for free, if it’s a few stl files and jpgs you’ll easily fly under the limit where you have to start paying.
As for previews, I think that’s harder to do especially for 3D files. I have a mac and have a folder which is mirrored to the cloud (using Google File Stream I think it’s called, which us just a mechanism to keep my hard drive and Google Drive sync’d) and various plugins for Finder (google ‘quicklook’) for stls and so on but most of them are unmaintained and now incompatible or a total faff to install but that gives me previews of things but does mean I have to have the data on my hard drive as well as in the cloud. There’s software for previews but you have to load the file, it’s not a thumbnail in a browser.