Greetings. I have successfully used the iCloud sign out / sign in to fix the photos not uploading. To your question -- in Photo Preferences > iCloud -- I only have the last box checked (Shared Albums). I do not have the following boxes checked: iCloud Photos and My Photo Stream.
I have 90,000 photos and over 100 videos which together takes up about 1TB of space. I just upgraded my iMac to a 4TB Solid State Drive so I would have enough room for my photos, software, documents and "room to grow." I load all my photos from the camera to my iMac. They are stored on the iMac, in the cloud and on an external Time Machine. I have NO photos moved from the cloud to my Mac laptop because the drive is to small. I have all the photos moved from the cloud to my iPhone, but only the thumbnails, so they take up less room. Pictures I take with my iPhone are uploaded to the cloud and then too my iMac.
Bottom line, I don't think it matters what you have checked in Photos Preferences.
I think one of the issues with the slowness of the process is if folks have more than one Mac computer. Uploading photos from the cloud to both an iMac and a Mac laptop would require a bunch of time, depending on the number of photos and videos, their resolution, the length of videos, your internet speed, etc.
A hint at what you might face next, AFTER you have uploaded all of your photos. The next thing my computer did was to scan the faces in PEOPLE. You can watch it happen by opening Photos and then clicking on People. Scroll to the bottom of that page and it will give you an update. It took over a week for my computer to scan through all 90K photos. HINT: In order for this to work you have to leave the Photos software turned OFF but your computer turned ON. Let your computer run 24/7 if possible and didn't let the computer go to sleep automatically.
Lastly, the issue now is that all the edits I made on individual photos since before I installed Catalina are "gone." The edited thumbnail photos still show the edited symbol (three horizontal sliders) and they look like the edited version. However, if you click on the thumbnail, then click on EDIT, what you see (if your Mac is like my Mac) is the unedited, un-cropped original photo as it came out of the camera. If you export that photo you get the unedited version. If you don't edit that photo and just click Done, the resulting photo, and the thumbnail, show the edited photo. Weird, I know. I'm hoping that the software revision that's coming will download the editing commands from the Cloud back to the computer.