I didn't set a max width on purpose. Take the following example:

Select Registration Date. If I set a max-width of 150px, it's not enough space. On multilingual sites, I have no idea what width may be required.

If I set the max width to 300px, then some o the dropdowns will simply be too wide, like Select State. The difference between J3 and J4, is that J4 uses a large default font size, thus taking up more space, but much easier for people to read.

@mbabker select element is controlled by the browser, why shall we override the default behaviour with some hardcoded width (which most probably will bring more problems than the one supposed to solve)?

It's not the lack of a max width that's the issue to me. Watch the video please, the element changes size depending on what you have selected; the native <select> doesn't do that.

This only applies to the chosen select boxes which you're using in com_patchtester, which we've nearly completely removed in J4.

We're still waiting for choises.js to release a beta with the feature that Dimitris requested.

I'd suggest you use the custom-select class for your select boxes

I copied the markup direct from a rendered com_content page (patch tester doesn't use legacy MVC so it doesn't use native search tools stuff). https://github.com/joomla-extensions/patchtester/blob/master/administrator/templates/atum/html/com_patchtester/pulls/default.php

Looking again, it looks like I'm still loading some extra JavaScript though and that might just be the only problem to fix for my case here.

Replace:

\JHtml::_('formbehavior.chosen', 'select');

with:

\JHtml::_('formbehavior.chosen', '.advancedSelect');

Chosen's gone completely. I just hadn't removed the JavaScript loader for it is all. Works fine without it.