Version 3.8.x of Moodle's PHP Max version is PHP 7.3, I thought. You've PHP 7.4.x.
See: http://www.syndrega.ch/blog/#php-and-dbms-compatibility-of-major-moodle-releases
There are some settings for global search in:
admin/settings.php?section=manageglobalsearch
Searchable courses
If set to search within enrolled courses only, course information (name
and summary) and course content will only be searched in courses which
the user is enrolled in. Otherwise, course information and course
content will be searched in all courses which the user can access, such
as courses with guest access enabled.
Include all visible courses
If enabled, search results will include course information (name and
summary) of courses which are visible to the user, even if they don't
have access to the course content.
MIght search web server error logs - mysql has gone away or similar + PHP time for a script to run or memory a script can consume. Blank screens returned to user usually means some resource/setting exhausted or too low.
Also, turning on MySQL logging full time and not ever turning it off could lead to some issues.
One can turn that on, watch in realtime (multitail), then turn it off:
slowlogon
# to turn on:
mysql -e ‘set global log = 1′ -u root -p’pass’
mysql -e ‘set global log_slow_queries = 1′ -u root -p’pass’
mysql -e ‘set global slow_query_log = 1′ -u root -p’pass’
multitail -i /var/log/mysql/mysql-general.log -i /var/log/mysql/mysql-slow.log;
The multitail line will show in realtime.
slowlogoff
# to turn off
set global slow_query_log = 0
set global log_slow_queries = 0
set global log = 0;
'SoS', Ken