You're probably looking for Material Design You apps, right? Here's a list of them. However, they are not from LineageOS. Just check out options marked with "FOSS".
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Interesting...
To be honest, I don't understand much about how the theming works. Do they use dynamic icons these days instead of being defined one by one in icon packs?
That's hard to answer. The app you're talking about (Markor) is probably still stuck on Material Design 1, or something even older that I'm not aware of. Material Design 2 is a slight improvement. MD3, also known as Material Design You is a completely different UI/UX guideline. When you're talking about colors and accent, as in, adhering to the system's preferences, that's called Dynamic color. I'm not sure if it's a MD3-exclusive, or if it's also available to older MD versions.
I see... Thank you for your answer. This is all new to me.