A hotkey (for example Shift+M), that opens a search bar with context menu for auto completion of ritual searches for the ritual diviner.

Examples:

Searching for the Ritual of the Full Spring:
This ritual creates a water source.
It could be searched with the following keywords:

• Water, Spring

Searching for the Ritual: Serenade of the Nether:
This ritual creates a lava source.
Keywords:

• Lava, Serenade, Nether

Searching for the Ritual: Well of Suffering:
Ritual to generate LP from mobs.
Keywords:

• LP, Well, Suffering, Mob, Sacrifice

ETC.

I would rather change it to bring up a UI element (not a proper GUI) that you can scroll through.

My thought was that scrolling becomes a nuisance once there are enough rituals (it already is for me, constantly left and/or right clicking while sneaking).

Having a UI element like the Sigil of Holding right now would require meaningful icons.
Having a UI element that displays a list of names to scroll through is probably not aesthetically pleasing (it would just be a wall of text).

That being said, scrolling is definitely better than left/right clicking in my opinion.

I would rather change it to bring up a UI element (not a proper GUI) that you can scroll through.

Wheel menu? Although that would be a really big wheel.

A good start would probably be to make sure that the Rituals are sorted (alphabetically) if that's not already the case?

UI element should be small and not obstructive. maybe something in the bottom left corner?

Need an idea for a meaningful identifier for each ritual (Kanji? just kidding), otherwise it will just be a variation of "scrolling through text".

They are sorted in terms of size. Earlier game rituals will appear first.