Formatting toolbar
Trilium allows two different editing experiences for text notes, based on your preference.
The type of formatting toolbar can be changed by going to Options and then looking for the Text Notes section. In it, look for the Formatting toolbar category.
Floating#
The floating bar is a more minimalist option, in which the formatting is hidden behind two different popups.
Block-level popup#
The first popup is the block-level popup. This will appear to the left of the current paragraph you are currently editing, as a sequence of dots:
Clicking this popup will reveal the formatting options that are specific to the entire paragraph, such as setting a heading, lists, tables, etc.

Inline popup#
The inline popup appears automatically when selecting a text:

All the options here apply only to the selected portion of text, such as changing the font size, or making the text bold.
Fixed#
The fixed formatting offers a more traditional editing paradigm, usually useful if a lot of formatting is needed.
All the options are combined into a single toolbar that will appear as part of the Ribbon.

By default, if the toolbar does not fit on the screen, the rest of the options will be grouped into a single option at the end. It is possible to display items on multiple lines by checking the corresponding option in the Formatting toolbar section.