@1005267334934 This is terrible! After doing some testing, I'm actually not sure that I'm seeing all the festivals either. Also, when I open the calendar, not all of festivals and events are displayed. I did just get a notification for the Flea Market but it doesn't show on the calendar. Anyway, I found two separate existing threads for these. If you think this is what you're seeing in your game as well, please click "Me too" on the first post and add any comments you feel are pertinent.
https://answers.ea.com/t5/Technical-Issues-PC/Festivals-not-occurring/m-p/8956933/highlight/true#M171652
https://answers.ea.com/t5/Bug-Reports/OPEN-CL-Festivals-Don-t-Appear-in-Calendar-Until-Festival-Begins/td-p/10526468
If you have added a restaurant from Dine Out to a lot in San Myshuno, this appears to create an issue with festivals also. There is a thread for that here.
https://answers.ea.com/t5/Bug-Reports/OPEN-CL-DO-CD-GTW-Business-lots-keep-festivals-stalls-from/m-p/6396299/highlight/true#M45186
If your sims are living in SM, try traveling to another world and travel back to the festival location.
Lastly, perhaps you could try having your sims travel to festival / event locations to see if they're happening anyway.
Carl's has a good list of City Living festivals here...
https://www.carls-sims-4-guide.com/expansionpacks/cityliving/festivals.php
The Gamer has a guide to Snowy Escape festivals here...
https://www.thegamer.com/the-sims-4-snowy-escape-festival-guide/
If you have Cottage Living, it looks like those are the only ones consistently appearing in my calendar. There is a different fair every Saturday from 3:30 pm to 9:30 pm.