LinkedIn has no bold button, so styled text is made of Unicode characters you paste in. Pick the field you are writing for, style all of it or just one line, and see it laid out the way LinkedIn will lay it out.
Ctrl+B, Ctrl+I and Ctrl+U work as you would expect, with Cmd on a Mac. Remove formatting turns styled characters back into ordinary letters, which is the fix once you have bolded something you now want people to be able to search for.
The preview draws the line where LinkedIn stops showing your text. Getting above it is a writing problem more than a counting one, and a few things help.
Then read the grey text in the preview. If the part you care about is down there, move it up rather than trimming words off the top.
Styled text buys you emphasis in a field that has none. It costs you searchability and it costs you readers on a screen reader. Which field you are in decides whether that trade is worth making.
In a post, it usually is. One bold line at the top works as a heading, and nobody goes looking for the body of a post in a search box.
In your headline, your About section or a job title, it is usually a mistake. Those are the fields recruiters search, and a styled word stops matching what they type. Leave the nouns alone and style nothing that somebody might look for.
Writing for somewhere else? On Instagram the problem is blank lines rather than bold, and the Instagram line break generator handles it. For Facebook and Messenger, use the Facebook text formatter. Every platform’s cap and cut-off sits in one table on the character limits page.
At about 140 characters on a phone and about 210 on a desktop, after which the rest is folded behind a "see more" link. The preview draws that line on your own text, and the grey part below it is what nobody reads unless they choose to. The cap is 3,000 characters, but the cap is almost never the number that matters.
LinkedIn strips formatting out of posts, so there is nothing to press. What every LinkedIn bold tool does instead is swap your letters for Unicode characters that were drawn bold to begin with, so the styling travels inside the text and survives being pasted in.
Reach, no. Searchability, yes: to LinkedIn a bold letter is a different character from the plain one, so a styled word no longer matches what somebody types into the search box.
Poorly. Depending on the reader, a styled word is spelled out one Unicode character name at a time or skipped over in silence. Anyone using one will get either noise or nothing where your emphasis was meant to be.
No. These are ordinary Unicode characters, the same kind as an emoji or an accented letter. The risk is your readers rather than the platform: a whole post in script is harder to read than plain text.
Yes. Be aware that your headline follows you around the site, appearing under your name on every post and comment you make, so a styled one is far more visible than a styled post and far more likely to read as shouting.
Select the part you want back and press Remove formatting. Undo works too, as do Ctrl+Z and the usual shortcuts.