in an itemized list you want the following: level 1 has no indentation, level 2 has 20 mm, level 3 has 20 mm more than level 2. Therefore you do this: * use the toolbar icon for mullets, then set the checkmark to specify relative values * for level 1 set 0 mm, for level 2 20 mm, for level 3 also 20 mm * for the width you set in all cases 10 mm result: it is impossible to get 20 mm indent for the second level. here are several attempts, for all of them the preview looks exactly as i want to have it, but I never get this layout as result. The first attachment shows an attempt to apply to the current selection. The second attachment shows an attempt to apply to the current selection using the properties dialog, not the toolbar. The third attachment shows an attempt to apply to the current selection and selecting the whole list in advance. Now one gets at least some indentation, but not the desired one. The forth attempt is to apply the change to the slide but as you can see, my setting is reset to apply to the selection instead of the slide. The fifth and last attempt was to not use relative values, but the dialog does not allow you to use more than 20 mm as value. Maybe I am too untalented by I tried now 2 hours (sic!), asked AIs, searched help forums. It cannot be that such a basic feature is not working. As I had problems with LO 26.0.2, I downgraded to 25.8.4 so all i report here is for the official Windows build LO offers at the website as latest "fresh" version. You can see that bug 170463 is also in that build.
Created attachment 205183 [details] screencast first attempt: apply to the current selection.
Created attachment 205184 [details] screencast second attempt: apply to the current selection using the properties dialog, not the toolbar.
Created attachment 205185 [details] screencast third attempt: apply to the current selection and selecting the whole list in advance. Now one gets at least some indentation, but not the desired one.
Created attachment 205186 [details] screencast forth attempt: apply the change to the slide but as you can see, my setting is reset to apply to the selection instead of the slide.
Created attachment 205187 [details] screencast last attempt: it is impossible to set a value larger tan 20 mm
While investigating bug 170493 I found a workaround: * after making the changed on the properties dialog one must press the button to decrease the indentation (despite it is shown as being zero. result: see attachment 205190 [details] so some "magic" indentation is added but at least the list looks then as it should. I am baffled.
The dialog has the option "Slide" and "Selection". If you have used "Selection" but no paragraph selected, then the list setting is only applied to the one paragraph where the cursor is. If you want to make a general setting for the master slide, you should not use the Bullet-icon but customize the list in the "Outline 1", "Outline 2" ... presentation styles. I think it would be better, to first discuss the problems on the Ask site, to sort out what is really a bug in the implementation and what needs a better description in the help and guides.
I have played a little bit with that dialog. It really acts sometimes unreliable. Especially resetting something does not work smoothly. But for a proper bug report "sometimes" is not precise enough. In regard to the paragraph indent: Impress uses old-kind lists. There a paragraph indent is add to the position of the list item. The numeric field for indent in the sidebar seems to work in this regard and you can see the additional indent in the ruler. The increase-decrease buttons seem not to work.