Sharing to social media cannot be scheduled. Sharing can be done when sharing immediately.
The post should be schedule to be posted the social media options selected and show in the scheduled tab
An error message is produced “Scheduling share failed. Please don’t be mad.”
Tried with just one social media selected (error is given with each), tried with or without a comment added. Social media has been disconnected and reconnected and the error still occurs.

#user-report
I just tested this, and can confirm this is happening with me too.
Reported in 934917-zen
The user in 934917-zen that Cena cited above is also not able to schedule posts via their wp-admin -- I'm not sure if that is relevant information?
When I try to test scheduling a publicize message for a post I end up with this in my browser console which will hopefully be helpful in tracking it down.

Reported in 919734-zen
Reported in HappyChat with user researchdigestblog. (They also requested to be notified when this is fixed, if possible.)
cc @artpi and @lamosty who previously worked on the Republicize feature.
Previous changes to that feature: #20912, #20921
Another user reported this here 1686129- HC and wants follow up here 933644-zen
This was fixed yesterday with #22064.
Most helpful comment
This was fixed yesterday with #22064.