As far as I remember Bootstrap does not support a "state" for their tabs.

Can be a feature request, but I doubt that it will get much attention.

Bootstrap doesn't support that natively, sadly. https://getbootstrap.com/docs/5.0/components/navs-tabs/#javascript-behavior

I am not sure we would want to implement our own solution for that in core on top of bootstrap. (Maybe? Maybe not?)

But perhaps a session cookie in your extension would do the job for now?

In my extensions, I just use a simple if else command like below:

if ($isJoomla4)
{
	$tabApiPrefix = 'uitab.';
}
else
{
	$tabApiPrefix = 'bootstrap.';
}

Then replace bootstrap. in original code with $tabApiPrefix variable, works well for me.

I opened the issue because in Joomla 3 it works. So I was wondering why it doesn't in 4. Even the tab state script is there https://github.com/joomla/joomla-cms/blob/4.2-dev/build/media_source/legacy/js/tabs-state.es5.js, but it doesn't work when I load it the same way as https://github.com/joomla/joomla-cms/blob/3.10-dev/libraries/cms/html/behavior.php#L895. So for me it looks like a compatibility bug.

Since I was the one that removed that script let me explain the reasons for that action:

• The script was jQuery and nobody wanted to vanillify that code
• The code was extremely inefficient. It was using XPATH for traversing the DOM and the whole logic was happening AFTER the normal BS logic
• The code was also loading a polyfill (total size, jQ+BS+tabastate ~300kb, the new tabs/accordion with the tab state logic is less than 10Kb)
• The code exists in the legacy folder so if someone wants to use it all it needs is 3 lines:

HTMLHelper::_('behavior.jquery');
HTMLHelper::_('bootstrap.tabs');
HTMLHelper::_('script', 'legacy/tab-state.es5.js', ['version' => 'auto', 'relative' => true], []);

So, should the project resurrect the old HTMLHelper behaviour?
I'll vote against it as it's already possible with 3 lines of code, but as the folder that holds that script denotes it's legacy and probably nobody should use it.

My 2c

I tried

HTMLHelper::_('behavior.jquery');
HTMLHelper::_('bootstrap.tabs');
HTMLHelper::_('script', 'legacy/tab-state.es5.js', ['version' => 'auto', 'relative' => true], []);

and it doesn't work. That's why I opened the issue. Not to revert the changes and load the bloat, but because it is not working the expected way with the legacy code.

and it doesn't work.

Ok, so when the project decided to use BS v5 should have updated that script as well. It should be a simple search/replace IIRC:
Search data-toggle
Replace: data-bs-toggle
Eg: