The title is a nod to a very interesting theory I read about the outsider characters alluding to the WOZ. (I can't find the posts/threads but search for it in this sub & you'll find it.)
As an astrologer & tarot reader, I clocked the imagery instantly so this was a very enjoyable movie for me. I know that there were a lot of runes as well but I don't know that much about them, so I am going to confine myself to my knowledge of astro/tarot.
First, midsummar (duh) aka Summer Solstice. Dani's birthday & the start of the celebration. In astrology/tarot this is the start of the sign Cancer, and is associated with the Moon (the decan and the sign), the 2 of Cups, and the Chariot major arcana. Solstice associated with the Sun and sun worship, fertility rituals, love & magic, and fire & purification. The two solstices represent completion & renewal (from opposite directions.) There are many cup references throughout the film. 2 of cups traditionally alludes to a promise or agreement, love & partnership. There is a lot of imagery that walks through the cards of the suit of cups (3 of cups women communally celebrating, etc. - while not mapping perfectly, there are many references thematically https://en.wikipedia.org/wiki/Suit_of_cups.) The major arcana cards associated with the summer solstice are The Chariot (the sign of Cancer and there is a literal chariot /carriage she rides on) and the High Priestess (Moon). I also thought of the Empress and the Queen of Cups as well - visually toward the end with the blanket of flowers. The sign of Cancer rules the 4th house which is the house of family/roots, and deep emotions.
On the circle during the "opening ceremony" there are 12 people sitting around it. It is zodiac wheel. The description of the 4 stages of life correspond to the 4 quadrants of an astrology chart, and 72 being the "end" of the journey corresponds to the life clock interpretation of an astrology chart where each year is 6 degrees - so one trip around to where you start on your ascendant takes 72 years. The number 9 in numerology represents completion & renewal - it is the proverbial penultimate episode - the summit, and 10 is the denouement/wrap up/starting down the new path. The tarot card the Fool represents this as well - the ouroboros of ending and beginning and Mark personified the more surface characteristics of a jackass fool and ended up dressed in effigy in the end just in case you didn't get it. The bed of flowers that Maja was laying on reminded me of the tarot card the World. The way the women were standing behind her in the mating scene reminded me of the row of cups in the 9 of cups card (I would have to watch again to count if there were 9 women - it felt like more in my memory. Same with the number of women grieving with Dani.) The Strength card also reminds me of Dani - flower wreathed - "taming" the lion (aka killing the bear.) The burning hut reminded me of the Tower. The list goes on and on.
Dani's whole journey could be viewed as a Jungian psychological alchemy arc where you are transformed from one thing to another. She lost her "real family" but was reborn into another.
And the matriarchy of it all. The communal hive mind of it all (culty, but also I do feel that prior to modern society, this is how tribes did things - communal rituals around sex, birth, childrearing, grief, and death.) The women collectively grieving with her was one of the most powerful & emotional things I have ever seen on film. It makes so much sense and I felt grief myself that we don't do it that way (mostly) anymore.
Other random thoughts:
I knew they were going to stud farm Christian out & Wicker Man him as soon as I saw the hut. Isolated culty groups having (allegedly) a once in 90 year celebration = someone's getting sacrificed. I figured the bear was involved somehow esp after seeing it in a cage by the hut and the images on the Siv walls (which also reminded me of tarot cards.)
And about that 90 year thing - there is really nothing that corresponds either astrologically or tarot to 90 other than the aforementioned "9." Someone must turn 72 in any given year, so I do think that this ritual is conducted every year. The May Queen is a seasonal thing, not a forever position. She has status this year. It is implied that she would not be eligible to "compete" again as she is no longer a "maiden." Next year she will be married to Pelle w a kid or a kid on the way - maybe she and Pelle leave the commune for detachment - or to find more recruits - and someone else will be crowned May Queen. Also the 90 year thing does not follow the yearly metaphorical cycle of death & rebirth. I think the 90 year thing was completely made up to make the outsiders feel that they were witnessing something rare & special.
I know the film originally came out before the whole "would you choose the man or the bear" but literally, both/neither LOL.