Which theme am I using, after changing the cursor color? If I don’t save the new settings as a theme, I’m not using any of them.
And that’s wrong. macOS, Scrivener, this forum. Three already.
A modified “Standard” I suppose.
Which theme would I click in the menu to assign that color again?
(There is none that would do it.)

Which theme would I click in the menu to assign that color again?
Since you chose not to save your changed color you can pick any of them.
None of them would match that color. Because I didn’t save a theme after changing it.
Right? That’s the beauty of throwing stuff away. It’s gone. Doesn’t mean it didn’t exist before, though.
I think (might be wrong) what you’re trying to say is that it’s not a theme unless you change something, put a name on it and save it.

I think (might be wrong) what you’re trying to say is that it’s not a theme unless you change something, put a name on it and save it.
Current settings are not a theme, period. They can be saved as a theme for later retrieval, but I do not, hence I am not using the feature. Scrivener has hundreds of settings related to features I do not use.

Current settings are not a theme, period.
That’s as true as the statement “the world doesn’t exist when I close my eyes”.

They can be saved as a theme for later retrieval, but I do not, hence I am not using the feature.
The L&L team did exactly that for you. It doesn’t start to become a theme when you save it. It’s also not possible to not use a theme, no matter who saved it or how you call it, the moment you launch Scrivener.

Scrivener has hundreds of settings related to features I do not use.
They’re still there. And unlike the (default) theme, you can choose to ignore them.
Just bought a new macbook pro, installed scrivener, and i can’t find the Use Block Insertion Point option anywhere. I’m pretty sure I’m looking in these same menus but I just can’t see it. Has it moved? Thanks!
This feature has been removed in Mac OS 14 and newer, due to changes in Apple’s underlying toolkit. https://forum.literatureandlatte.com/t/scrivener-3-3-2-for-macos-released/136392
That’s too bad. Of course it’s a little thing and won’t keep me from using Scrivener. But I did love the block insertion cursor. FocusWriter has been able to keep it, though I think the color is no longer customizable (I’m remembering that it was for that app, but I could be wrong). But I don’t know how software development works and I guess there must be a good reason it wasn’t working for Scrivener (I’m getting a Page Not Found clicking on the link you posted there)
Ah, sorry, I sent you to an internal discussion by mistake. It’s in the version 3.3.2 release notes: Release Notes - Literature & Latte
FocusWriter isn’t a native Mac program, though. It is written in Qt, from what I can see, which is the same cross-platform toolkit we use to make Scrivener and Scapple for Windows (in theory we could make a Mac version of these!). It is indeed possible to set the cursor width in Qt, and this option remains available for Windows users.
Cross-platform software aside (which probably accounts for more software on your system that you might think), it is also possible for old software that hasn’t been updated to the modern Mac development toolkit to still exist, for older Mac projects that are still running deprecated functions, to use the old cursor, and for software that runs in a terminal emulator to be different, too. MacVim and Emacs, for example, or even Terminal.app itself, can still set a block cursor. Obviously these are not using the native Mac text engine though.
Further reference:
I just updated to Sonoma, and I am using Scrivener 3.3.3 and the cursor is huge and blue. I’ve spent the last hour trying to get it back to normal, testing editing text other apps, and it seems Scrivener is the only app so far that has a cursor problem. It’s very distracting and I’m struggling to find my writing groove staring at the big blue pill. I see this update in 3.3.3, but it doesn’t seem to work for me? Fixed some issues with the size of the new text cursor on Sonoma. [huge cursor…