Jacques Bédard 
The issue you are currently facing is most likely caused by a set of corrupt user settings which prevent Studio to start; the fact that you're seeing the same problem after reverting to the previous version also points to that root cause.

Can you please navigate to this location on your machine:

C:\Users\%username%\AppData\Roaming\Trados\Trados Studio
(if you copy this above-mentioned path in Windows Explorer it should take you to that location)

and rename the "Studio" and "18" folders found there to "Studio _ old" and "18 _ old"

If this doesn't do the trick, navigate to the "Documents" folder on your machine and rename the "Studio 2024" folder found there to "Studio 2024 _ old".

I have also raised a Support Case on your behalf if the resolutions I provided here do not work \ Support Case Id : CS0020655.

If you've managed to resolve the issue though, please let us know so we can close the Case from our end; otherwise one of our Engineers will reach out to you.

Best Regards,
Vlad 

Thanks for your answer. I was wondering how I would ever get a solution, since there is no simple path to getting any troubleshooting help on your website (on which website? Trados? RWS? RWS Community?) Well, I wouldn't call any of the solutions suggested a smooth update process. 

Why, in the first place, are user settings being corrupted by an update (yes, a few seconds before the update, everything did work fine)? If the problem is the customization of user settings, why should we be offered the option? 

If the problem is the presence of a few plug-ins (Antidote, Wordlight), why keeping the RWS AppStore icon on the quick-access bar (each time I try to get rid of it while customizing, it keeps reappearing)? 

Also, FYI, my hardware is almost brand new, not so recent as to having unexpected bugs popping up, but just recent enough to know for sure it works smoothly and so, for a couple of months now.

Before receiving your answer, I went through a few hours of scanning the messages on RWS Community, finding what seemed to be solutions, to no avail, and trying time and again the so-called solutions, ending up having no "reaction" at all from the application, it wouldn't even start. I did rename the "Studio 2024" folder, but I had to reinitialize my license manually off-line/on-line, download the previous version, reinstall it, reactivate my license, reinstall the update (hoping for the best). Let alone the fact that I was very methodical, uninstalling the application, restarting my PC, reinstalling the application, restarting my PC, and so on. 

Now, the application is running, updated, and I'm starting the customization process all over, hoping I'm not corrupting anything. Then, I'll reinstall a few plug-ins. I must stress that I reported the customization bugs of the ribbons and the quick-access bar quite a few years ago, and reported it again when installing my new Studio 2024. Still, some options/icons I don't use and tried to remove keep coming back, and some icons I would need don't show up.

To sum up, a very valuable tool, but the activation/reactivation, update and customizing processes are very cumbersome, at least for a freelancer that doesn’t have a TI department handy.

Thanks for your answer. I was wondering how I would ever get a solution, since there is no simple path to getting any troubleshooting help on your website (on which website? Trados? RWS? RWS Community?) Well, I wouldn't call any of the solutions suggested a smooth update process. 

Why, in the first place, are user settings being corrupted by an update (yes, a few seconds before the update, everything did work fine)? If the problem is the customization of user settings, why should we be offered the option? 

If the problem is the presence of a few plug-ins (Antidote, Wordlight), why keeping the RWS AppStore icon on the quick-access bar (each time I try to get rid of it while customizing, it keeps reappearing)? 

Also, FYI, my hardware is almost brand new, not so recent as to having unexpected bugs popping up, but just recent enough to know for sure it works smoothly and so, for a couple of months now.

Before receiving your answer, I went through a few hours of scanning the messages on RWS Community, finding what seemed to be solutions, to no avail, and trying time and again the so-called solutions, ending up having no "reaction" at all from the application, it wouldn't even start. I did rename the "Studio 2024" folder, but I had to reinitialize my license manually off-line/on-line, download the previous version, reinstall it, reactivate my license, reinstall the update (hoping for the best). Let alone the fact that I was very methodical, uninstalling the application, restarting my PC, reinstalling the application, restarting my PC, and so on. 

Now, the application is running, updated, and I'm starting the customization process all over, hoping I'm not corrupting anything. Then, I'll reinstall a few plug-ins. I must stress that I reported the customization bugs of the ribbons and the quick-access bar quite a few years ago, and reported it again when installing my new Studio 2024. Still, some options/icons I don't use and tried to remove keep coming back, and some icons I would need don't show up.

To sum up, a very valuable tool, but the activation/reactivation, update and customizing processes are very cumbersome, at least for a freelancer that doesn’t have a TI department handy.