Welcome to Android Central forums.
Have you tried changing your font? At least in the first screenshot it looks like you're complaining about the lower portion of the text being cut off. That could be due to the text height.
In the last image is a bit more confusing because the chevron for expanding the box is full and present while the words are cut off. Since it only appears to be affecting the words and not the chevron it again seems like a font issue. Did you try touching the chevron and expanding the selection? What is the result of that?
Besides using what looks like a Comic Sans font, have you intentionally increased the size in your settings? On the S24 navigate to Settings>Display>Font size and Style, try moving the slider to the Left 1 or 2 sizes, then check if this allows you to use the Comic Sans font you want or try a different, more standard type set font type. See if it is just the nature of that font.
While the initial screenshot from Reddit talks about Facebook these later screenshots do not look like FB. Are they Reddit or something else?
What keyboard are you using?
I've gone into Reddit and tried adding a comment and I get a whole huge text box but I may not be in the same app, or trying to leave comments in the same way as you are. Please describe when and how you are seeing this. For example, I open the Reddit app, see a topic I want to comment on, tap the comment bubble at the bottom of the page, my keyboard opens in a small slit of a text box just above the keyboard, except tell us how you do it. You can see my result below following those steps.