Outlines - the one thing I'm missing

Outlines in Obsidian are very powerful!

The only thing I’m missing is a specific folding action:

What is the easiest way to fold the outline so that it only shows a, b, c, d (not a1, a2, b1, b2,…)?

In the outliner plugin, there is the function “toggle folding” for “Vertical indentation line click action.” For me, it only works in combination with “Draw vertical indentation lines” activated (Is that true?).

The problem with “Draw vertical indentation lines” activated is that it seems to be glitchy: When I fold headings with outlines, it renders it weirdly:

It should be without the vertical lines at the beginning of the headings. This is what it looks like when “Draw vertical indentation lines” is deactivated:

The problem now: toggling folding for the outlines doesn’t work anymore.

My Question: what is the easiest way to toggle fold outlines as discussed above - without the glitchy rendering? (I use the default theme)