CTRL+U > CTRL+F > max_file_size = 2097152b, which means exactly 2 MiB. Too bad the attachment tab doesn't say so itself - even adding a file being bigger than this won't tell in the error message the limit. Created ticket PHPBB3-15300 as an improvement request.
"The problem is probably not my English but you do not want to understand correctly. ... We will not come anybody anyway, nevertheless, it's best to shit this." Affin, 2018-11-20 ↑
"But this shit is not here for you. You can follow with your. Maybe the question, instead, was for you, who know, so you shoved us how you are." axe70, 2020-10-10 ↑
"My reaction is not to everyone, especially to you." Raptiye, 2021-02-28 ↑