Niigo didn't get a lot of mixed events after 4th anniversary so they weren't hit with "not really relevant mixed" beam that much. Ill go by chronological order for convenience

Exciting Picnic – really important event focusing on Mizuena. It happens right after secret distance, it tackles the gap between mizuki and ena (due to secret) and how they cling to each other anyway, going faw and beyond to help each other. Bonus is really delightful shizuai and really funny ruinene with their B-plot to become buff

Summer festival is a Shinonome event and siblings event are pretty important for both of them. About complicated relationships between Akito and Ena. Its really good even if youre not really much of an Akito person.

Intersecting melodies is a kanamafu mixed so it should be really important but im being really honest – I remember it very badly and haven't reread in.......2 years? So I cant really speak of its value. I think you can put this one for later

Kamiyama cheering squad, despite being a Rui focus, is also vital Mizuki reading. You may or may not read it togehter with Mizuki's first mixed – Kamiyama festival. They work in tandem and provide backstory for these two and give a better understanding how they handle their loneliness and how they work as each others support system.

Spoyjoy is just really cute and really fun. Definitely read it but its not lore packed

Rainbow canvas is also really cute and while not something groundbreaking it further our understanding of enas relationship with art, which by that point, is still complicated

Festival tinged with twilight (NOT TWILIGHT PARADE) massively important Mafuyu focus, one of first times where her persona slips in public and you get to see her interact with almost full cast which is rewarding i think. Also has really important talk with Rui.

Raise this bow in Snow White World - BANGER of a mixed event, still the best one in my opinion and SUPPPERRRRRR important for mafuyu. Basically confirms that she has a disassociation method to relive her pent up stress. Shizuku is the focus so you get an outsider pov

Candles valentines nothing much important you can read it later

Standing next to Kind and Gentle You i think is a very solid honakana event it just focuses on their relationship and friendship and its really rewarding. But also could be read later, if you want.

Unchanging warmth if also a required mizuki reading. Her backstory + sister full appearance (she appeared first in escape for survival but here we get a proper story involvement)

Relax teatime you can also read someday later. Its pretty much just a hang out event

Beautiful sound isnt really that much of for niigo crumbs it really is a Toya focus shuffle but Wonderhorror is a different story and Mafuyu is an important part of a story. She learns that there are more ppl other than niigo who understand her situation and want to help (emu, shizuku, honami). Which is really sweet

Unfading wishing sort of a summer festival part 2 but new year and Ena here is less of an acting character and more of a reason for deepening Akito and Airi friendship.

Show your Shine and Put Your Heart into One Stitch you can read last tbh. They arent bad by any means they just not really important. Or exciting

You are my hero and Our Golden Days while also have niigo character dont really provide anything special as well. They just feel good events so you can also read them way later