Step 1: install XAMPP 7.4.1, make it work :) At this point you have C:/yourdir/xampp and in particular C:/yourdir/xampp/php and C:/yourdir/xampp/apache/conf/extra
Step 2 : download XAMPP 8.0.1, as a zip archive, not a self executable install Don't install it. Instead,
- extract the content of the xampp/php directory and put it in C:/yourdir/xampp/php8
- extract the file xampp/apache/conf/extra/httpd-xampp.conf and copy it to C:/yourdir/xampp/php and C:/yourdir/xampp/apache/conf/extra/httpd-xampp8.conf
Step 3 : edit C:/yourdir/xampp/php8/php.ini and modify the paths (eg replace all default \xampp with \yourdir\xampp).
