The one paragraph I currently have in that item is too long.
When working on a bulleted list or a numbered list, the “Bullets and Numbering” toolbar is displayed. (On my machine, it appears near the bottom of the window.) One of the icons on that toolbar is “Insert Unnumbered Entry”.
So, if you want a new paragraph but don’t want to assign a number or bullet to that paragraph, after finishing the preceding paragraph but not having pressed Enter, click on that “Insert Unnumbered Entry” icon in the “Bullets and Numbering” toolbar, and then you will be at the start of the unnumbered (or unbulleted) paragraph where you can start typing.
Then to resume the numbering or bullets, hit Enter and you will get the next number in sequence or the bullet.
If you set paragraph-specific settings like “Do not split paragraph” for the Format | Paragraph… | “Text flow” tab, it will be just the one paragraph that will be treated as being kept together, the numbered and unnumbered paragraphs being treated as separate paragraphs as far as this feature is concerned.
(Contrast that to, say, hitting Shift+Enter, which will treat the text above the Shift+Enter and the text below the Shift+Enter as all belonging to the same “paragraph”, so “Do not split paragraph” will put both the above and below text on the same page.)
There doesn’t seem to be a default key assigned to “Insert Unnumbered Paragraph”, but you could assign a shortcut key to this in Tools | Customize… | “Keyboard” tab, in the Functions (bottom half) select “Numbering” | “Insert Unnumbered Entry” (i.e., Category: “Numbering” and Function: “Insert Unnumbered Entry” are highlighted) and in the top half highlight the shortcut key you would like associated with this particular function, then click on the “Modify” button. However, before assigning a key, you may want to make sure that the key is not assigned, either as a LibreOffice keystroke or as a Writer keystroke, and you will have to click on the radio button for LibreOffice or Writer on the upper right part of the “Keyboard” tab. Since this is specifically something you want for Writer, when you are doing the actual assignment, I would suggest it may be better to do it as a “Writer” keystroke.
+1. Thanks for pointing this out. I forget about toolbar options as I mainly use styles. I have edited my answer accordingly.
With respect to your use of the word “in” in your question being taken as meaning “using the same style or definition”, this is possible via toolbar option, as show by @Mark12547. You can also style a continuing paragraph to be indented and have all the characteristics of surrounding list paragraphs, except for the un/ordered list item identified. Here is an example with the middle list item making use of the Text Body Indent style for two of the three paragraphs.
Very lengthy list items are generally indicative of an issue with content presentation. You may also want to consider styling the content differently i.e., use headings.