Reproduction steps - number 1:
Create a topic - nothing special, accept the defaults
Edit the topic
Modify the 'Publish' setting from 'Immediately' to some date in the future of your own choice
Save the change
Expected result
Topic has been modified to be published in the future, and can only be seen by those with permissions to see those type of topics
Actual result
The change isn't saved, and the topic is still visible to all who have permissions to view topics in that forum
Reproduction steps - number 2:
Create a topic, modify the 'Publish' setting from 'Immediately' to some date in the future of your own choice
Edit the topic
Modify the 'Publish' setting to a different date/time of your own choice
Save the change
Expected result
Hover over the icon displaying the 'To be published' information and the topic is set to be published on the new date/time
Actual result
Change isn't saved, and the publishing time is still set to the original value
Tested with PHP 7.4.30 on my test site, and PHP 8.0.21 & 8.1.8 on localhost test sites
Q: Are all applications/plugins disabled?
A: None are installed on the test site, and all are disabled on the localhost test sites.