Appears to be some js applying the following inline styling to the dropdown...

transform: translate3d(-9px, 37px, 0px);

It is that -9px misaligning the dropdown. Javascript is really not my forte, so I have no idea where that should be changed.

@ciar4n I can't even find the js that is doing that :(

It is

fileOverview Kickass library to create and place poppers near their reference elements

inside file
media/vendor/bootstrap/js/bootstrap.bundle.js

There was an issue to allow disabling these inline style via JS
so that people can customize positioning themselves

twbs/bootstrap#23378 (Popper.js messing up dropdown styles)
thus they added support for
data-display="static"
with
twbs/bootstrap#24092

So we can add data-display="static" after data-toggle="dropdown" to the layout file to disable it
and then use our custom CSS , to control positioning of the drop down

https://github.com/joomla/joomla-cms/blob/4.0-dev/layouts/joomla/toolbar/dropdown.php#L36

Documentation has not been updated yet ???
https://getbootstrap.com/docs/4.0/components/dropdowns/

You can see data-display="static" here:
https://github.com/twbs/bootstrap/blob/9f742114840e71fd6557ca4fca3dcaaf72452f6d/docs/4.0/components/dropdowns.md

then use something like

.btn-group .dropdown-menu {
    ....
    left: auto;
    right: auto;
    width: auto;
}

which will should also fix current positioning problem for RTL too

Thanks I will take a look at those links later

Documentation has not been updated yet ???

It has but this is only for BS 4.1 so the link is https://getbootstrap.com/docs/4.1/components/dropdowns/#dropdown-options

Updated PR and original post. Thanks @ggppdk for pointing me in the correct direction

I've tested before and once the patch has been apply with Patch tester and I've not see any difference.

The width could be just a little larger in order to correctly display the last letter with a little space to the right.

@cavo789 https://github.com/joomla/joomla-cms/tree/4.0-dev#how-to-get-a-working-installation-from-the-source

You can not use patchtester alone for testing if/when there are css or js changes as I wrote in the original post

I have tested this item ✅ successfully on 66ec5ee

I have tested this item ✅ successfully on 66ec5ee

Menu Box autosizes with text length as expected.
Also working in other views

Ready to Commit after two successful tests.

I have tested this item ✅ successfully on 66ec5ee

Thanks guys! Nice teamwork!

thanks