[Quoth]

Also I find it's best to NEVER use a list format, but a suitable paragraph style and manually put the bullets or numbers or letters, because ebooks are more limited in lists than HTML (has to start at 1 and not be interrupted etc).

Using LO Writer and an extra Save As in docx you can have a paragraph style with a box. It isn't a frame, but looks like one and survives even epub to mobi conversion (which surprised me as Mobi has only inline style & HTML3 no CSS). You are limited with how margins work.

Don't use actual frames. Naturally you can't have two boxes side by side, unless they are in table columns, but tables are notoriously poor on smaller screens or user picking larger font. They fail.