[shka]

It is only a MariaDB-reserved-word-problem with two possible reasons and solutions.

A. Install mod first and later upgrade MariaDB to 10.2.4+
Then you can check in phpmyadmin if there is a column "rows" in table formbits. If yes then backticks two posts above is the solution.
If no then B.

B. (like PPhysX) Install mod on MariaDB 10.2.4+
Then adding the "rows"-column fails in installer. Then it makes more sense to use a better column-name.
a. First goto phpmyadmin in forum-db
Call sql (same as installer but changed column to "textrows" for visible rows in textarea)

ALTER TABLE formbits ADD textrows int(5) NOT NULL default '3';

Then with sql "show fields from formbits" you shoud see a new line (= tablecolumn) called textrows

b. The go to forms.php and edit the three lines 1976,3305,3555. You can use old or new version (with or without backticks, but replace "rows" with "textrows").

c. Then edit some other lines (always replacing rows with textrows shown next)

line 2054
			textrows = '". $vbulletin->db->escape_string($rows)."',
line 3401
			'rows'          => $formbit['textrows'],
line 475
			$formoutput .= $form['prea'] . ($qo[$formbit[id]] >= $formbit['textrows']  ...
line 521
		elseif (($qo[$formbit[id]] < $formbit['textrows'] OR ...
line 1611
			$i = $formbit['textrows'];
line 2377
			$starti = $formbit['textrows'];
line 3314
					'" . $vbulletin->db->escape_string($question['textrows']) . "',
line 3564
					'" . $vbulletin->db->escape_string($question['textrows']) . "',