I have the same exact issue and it started today (wasn’t there a day ago). I usually manually review all updates and apply them as I see fit. However, a few minutes ago I went to do that and all the UPDATE/OPEN buttons are missing just as shown by LUKATIBO.
I can the the UPDATE or OPEN button (if app has already been updated) by going into the specific app tab/landing site. However, in the main list view they are gone.
I still have the UPDATE ALL at top of the list of updates, and also just like LUKATIBO, I still show the OPEN button in the main list for the apps that were updated on the day prior.
I too have restarted, force restarted, and signed off and back on on the APP STORE, but to no avail.
Mb the buttons will show up for the next app updates, and these will have the button missing just like the ones updated earlier still showed the OPEN button.
I will update hopefully by tomorrow if and when there are new updates.