Clock app showing blank and unresponsive interface in macOS Tahoe (26.0+)

I have been experiencing this since the latest Sequoia patches (15.4+) on my 2023 MacBook Pro with M3 Max, and, now, in Tahoe (26.0.1–26.1), the Clock app is completely broken.

Back in Sequoia, I started to notice a distinctive slowdown in the Timer function only: clicking on the green button to start a timer would not respond until, about 20 seconds later, as many timers as you clicked would appear, all started at the correct time. Pressing on 'Cancel' would get the same behaviour. The button would not respond or, better, it would respond about 20 seconds later. Here it is how it behaved in Sequoia:

https://youtu.be/EY0bkFSOb70

After updating to Tahoe (and it persists in 26.1), the Clock app is now unusable: the 'Local Times' tab '+' button takes a few seconds to respond but it works; the 'Stopwatch' tab apparently starts but there is no numbers on screen. Pressing the Lap button given a series of "0:00:00" laps; the 'Alarm' tab apparently works until, then, the alarm is not set; finally, the 'Timer' tab is just blank (or, well, black). No interface, nothing at all.

Here's a video of the issue in Tahoe 26.0.1 (same in 26.1):

https://youtu.be/z1R33m3Qf_o

I have already tried to reinstall macOS, without any progress.

In a new user account, both standard and administrator, the Clock app works flawlessly.

Through Apple Support we have gone through all the standard procedures: Safe Mode, clean the user and system library of all temporary files, launch agents/daemons, plus much more (including resetting permissions). I have an open ticket which is: 102729620952. The engineers sent me the CaptureData.dmg app and I uploaded the sysdiagnose file provided.

For now the advisor is suggesting to erase the Mac and start afresh but, using this Mac for work and seeing no issue outside of the Clock app, I am a bit reluctant to proceed in that direction. The previous advisor, which then disappeared without calling me on the appointed day, prompting me to look for further help, had suggested to migrate to a new admin user. While we never managed to get there, this is possibly where I will end up while the engineers try to find what is causing this. My only doubts are:

• I don't want to use Migration Assistant nor Restore from Backup because it would bring back all my user library, with the issue potentially included.
• I am not familiar with how to use the Public/Shared/Write Only/Drop Box folders and the Apple Support articles did not clarify it enough to make me feel comfortable using them.
• I could simply copy files to an external SSD, then copy them back. I am aware, though, that recent macOS has the new concept of "owner", meaning that I could get in troubles once I remove the old user.

Analysing the logs capture with both the Console app and the LogUI app produce results that, compared with a log from a functioning Clock app, show little to no differences.

I'm attaching the logs here: https://www.dropbox.com/scl/fi/hbaep9z6kk45lc6uwb7jw/LogUI-Clock-App-Malfunction.zip?rlkey=bapzjjp5mw9wn9jhqfw5np2rv&dl=0

What do you think could / should be done in this case?

Regardless of how this issue will be resolved, I would like to take the chance to thank you everyone who has already been helping me so far, even if to no avail.