I'm looking for a solution to limit the input length for the title of events (not the length of the output – this is possible in the settings).
If somehow possible with an override and without core hack.
I would like to add the maxlength HTML attribut to the input tag in
Not sure if you can override a JEM model, but if you willing to hack core JEM you are looking for event.xml file in administrator\components\com_jem\models\forms\ (backend event edit) and components\com_jem\models\forms\event.xml (frontend event edit) folders.
Find field name title (around line 28 or 18) and add maxlength="90"