Cathedral is still being renovated but you are allowed to go inside now.
St Marks' is not closed for renovations but the square it is on is closed for security reasons after someone fired a gun at the government building during covid.
In Zagreb there are a number of food festivals throughout the year. Pizza festival, Asian festival. I think burger festival is the most popular, it is essentially 10-20 street food stalls all set up in a park all serving hamburgers, with a central drinks stall in the middle. It is popular as a thing to do for locals. If you are feeling like a burger you could easily go to the park and try one. However Zagreb is full of good restaurants so maybe you will want to eat somewhere else instead.
I do not know much about the puppet festival but it looks interesting if you have nothing else to do, if you are there when they have a procession on the main sqaure that might be worth stopping for.
Those highlights are only okay to me, vendors on Dolac have moved ever since the roof fell in last year. Jelačić trg is just a square, Kraš is a good place to sit and watch people and have an ice cream. Stone Gate you just walk through. I do not even take visitors to Museum of Broken Relationships.
Museum of Naive Art is better but only maybe four rooms, I think they are moving to a bigger location soon. Klovićevi dvori is good depending on the exhibition, looks like it is first public presentation of donated art while you are there which could be interesting if you like art. Atelijer Meštrović is the home of Croatia's most famous sculptor, but his Split residence museum is more impressive. Zagreb City Museum is very good if you like history. I haven't been to the archaeological museum. Modern art museum is probably the best but it is in the suburbs, and other museums which I would recommend highly are closed for renovations, some after 2020 earthquake and some with EU funding.
I usually take visitors to parks and caffé bars. Sljeme is number one choice for traditional meal at the top of the mountain and then maybe a hike down. Maksimir is also a beautiful park for a visit especially if you have children with a zoo, lakes, big play area, and botanical garden is nice if it is open. Farther away parks, Bundek also has big play and swim area but I do not know when it closes and Jarun has an artificial lake for boat racing you can ride bikes around.
Note most things are closed Sunday, I think that usually does not include tourist attractions but check hours before your visit so you do not miss anything you would like to see and enjoy your visit to Zagreb.