I cannot test this on the new version of miniBB, but in the old one I have I get maximum topic text lenggth to be 100 even if I set $topic_max_length=250;

Be sure you have topic_title length in topics database also equal to 250. In old version, it was specified as varchar(100) it should be varchar(254) - or if you are on multilanguage forums with UTF-8 encoding, it's even better to specify it as TEXT.

Ok! I'll try! Thanks!

I have one suggestion: there should also be something like $text_max_length for File Upload Plugin in addon_fileupload_options.php This should specify text length in text comments to the photos&files.

This option is equal to $topic_max_length already. I think, specifying 254 for $topic_max_length is enough for most cases, incl. topic titles and file descriptions. These both values should be short and descriptive.