What happened?

1.A JavaScript runtime error occurs in the browser console on Joomla 6.1. The error is thrown inside the bundled Bootstrap/Joomla UI scripts and prevents correct dropdown behavior.

Uncaught TypeError: Cannot read properties of undefined (reading 'length')
at gt (dom.min.js?5.3.8:1:2558)
at dropdown.min.js?5.3.8:1:665

media/vendor/bootstrap/js/dom.min.js?5.3.8
media/vendor/bootstrap/js/dropdown.min.js?5.3.8

That occurs in frontend and in backend.

Additional context:
Bootstrap 5.3.8 changelog notes that the JS change in this version was:
"Revert: Attempt to return focus explicitly to dropdown trigger"
(https://blog.getbootstrap.com/2025/08/25/bootstrap-5-3-8/)
This reversion may have removed a guard that previously prevented gt() in
dom.min.js from receiving undefined, reintroducing this TypeError in Joomla's
dropdown initialization flow.

Version

6.1

Expected result

In backend, the dropdown button "Take a Tour" or "User menu" should work without console js error.

Actual result

The "Take a Tour" or "User menu" dropdown in the top of backend doesn´t work and the console displays the error:
dom.min.js?5.3.8:1 Uncaught TypeError: Cannot read properties of undefined (reading 'length')
at gt (dom.min.js?5.3.8:1:2558)
at dropdown.min.js?5.3.8:1:665

System Information

Joomla! 6.1.0 Stable [ Nyota ] 14-April-2026 16:00 UTC
PHP Version 8.4.10
Database Type mysql
Database Version 8.0.45-36
Joomla Backward Compatibility Plugin Enabled (classes_aliases:"1", legacy_classes:"1")

Additional Comments

That works in 6.0.x