steve228uk

Limit post titles with a character limit within the WordPress dashboard. The plugin works with default post types (posts/pages) as well as any custom post types defined by plugins or themes.
Simply set the character limit in the plugin’s settings pane and check which post types you wish to limit.
The title is limited within the dashboard only and pre-existing titles may need to be updated to match the new limit.

Limit Post Titles

Just wanted to let everyone know that this plugin does not work with the block editor (default editor since WP 5.0), so don't waste your time installing it if you plan to use it with the block editor

doesn't work with block editor

Limit post titles (including pages and custom post types) within the WordPress dashboard.

Atomicsmash

Works with ACF v4 and v5
This plugin provides an Advanced Custom Field textarea that limits the number of characters a user can add. The limit is cleanly represented by a jQuery Ui progress bar. You can define the number of characters on a per field basis.
This has been tested in:
<ul>
<li>ACF – Repeater fields</li>
<li>ACF – Flexible content fields</li>
<li>ACF – Option pages</li>
</ul>

Advanced Custom Fields: Limiter Field

This plugin provides a textarea that limits the number of characters a user can add. The limit is cleanly represented by a jQuery UI progress bar.

Limit Post Titles vs Advanced Custom Fields: Limiter Field