in the same PC is running php 7.3.33 and mysql 5.7.33
in my old env xoops 2.5.10
url /modules/system/admin.php?fct=users
when I access the page you will see the list of the user registered
if I press SEARCH button I can still see the list of the users
if I type 'ceca' (for example) and press SEARCH I see in list just one user (as it should be)
in the 2 new site in 2.5.11
where one is upgraded and one is fresh installed
same page url /modules/system/admin.php?fct=users
the behavior is the same for both new site
when I access the page you will see the list of the user registered
when I press SEARCH button the list is empy
If I search for a username I always receive not found and what I typed in the field disappear
Let me know if you need more info to troubleshoot
Carlo