Bootstrap 5 dropped the support for Internet Explorer. But there are still many areas in which IE is strongly represented. Doctors, craftsmen, lawyers etc., wherever older or non-technical users can be.
If the page is browsed by Internet Explorer, an alert is displayed below the navbar. Check this site here in Internet Explorer emulator.
This is done by a pluggable function in /inc/template-tags.php and can be translated.
If you do not want to display the alert, open header.php in child-theme and scroll to the bottom. There you will find this hook:
<?php bootscore_ie_alert(); ?>