I'm having this issue, too, and I'm wondering if it has anything to do with the fact I keep getting the "The festival is ending in 1 hour" notifications despite the fact my Sims are not at a festival. That would be considered a goaled event which is why its not letting me plan them right away.
@Krispicito Do you have screenshots that are less bright ?
Also found this older thread: https://answers.ea.com/t5/Bug-Reports/HSY-Can-t-plan-goaled-events-on-Fri-Sat-with-teen-in-household-1/td-p/13777139
and also this: https://answers.ea.com/t5/Bug-Reports/Can-t-create-goaled-event-on-top-of-another-event-on-same-day/m-p/13482111
I do still have that issue but actually it's Sat/Sun for me now.
EDIT: NVM. It seems it's when a holiday is taking place on that day. Deleting the holiday makes goaled events possible.
