Please help us help you and fill where relevant:
Your LimeSurvey version: master branch, LimeSurvey Community Edition Version 5.6.4
Own server or LimeSurvey hosting: local
Survey theme/template: none
==================
I'm trying to deploy limesurvey on my local to develop but same installation that works perfectly on windows doesn't work for survey pages and advanced --> themes pages on ubuntu.  it prints blank page on view with no error message for both page. List survey page and other pages works as expected. Only aforementioned themes page and survey page that comes after clicked on list survey doesn't work.
Installation completed without error messages

test:
GET http://localhost/index.php/surveyAdministration/view?surveyid=586152
500 Internal Server Error

test2:
GET http://localhost/index.php/themeOptions/index
500 Internal Server Error

PHP version: tested on 7.3 and 7.4 same result.
Apache Server version: Apache/2.4.29 (Ubuntu)
Mysql Server version: 5.5.5-10.10.3-MariaDB-1:10.10.3+maria~ubu2204 mariadb.org binary distribution

Apache2 log:
[Tue Feb 14 23:01:54.474206 2023] [mpm_prefork:notice] [pid 3044] AH00163: Apache/2.4.29 (Ubuntu) configured -- resuming normal operations
[Tue Feb 14 23:01:54.474224 2023] [core:notice] [pid 3044] AH00094: Command line: '/usr/sbin/apache2'
[Thu Feb 16 09:02:41.914699 2023] [mpm_prefork:notice] [pid 3048] AH00163: Apache/2.4.29 (Ubuntu) configured -- resuming normal operations
[Thu Feb 16 09:02:42.196728 2023] [core:notice] [pid 3048] AH00094: Command line: '/usr/sbin/apache2'
[Thu Feb 16 09:32:02.924779 2023] [mpm_prefork:notice] [pid 3048] AH00169: caught SIGTERM, shutting down
[Thu Feb 16 09:32:03.057150 2023] [mpm_prefork:notice] [pid 19649] AH00163: Apache/2.4.29 (Ubuntu) configured -- resuming normal operations
[Thu Feb 16 09:32:03.057216 2023] [core:notice] [pid 19649] AH00094: Command line: '/usr/sbin/apache2'
[Thu Feb 16 09:32:42.587889 2023] [mpm_prefork:notice] [pid 19649] AH00169: caught SIGTERM, shutting down
[Thu Feb 16 09:32:42.742566 2023] [mpm_prefork:notice] [pid 20500] AH00163: Apache/2.4.29 (Ubuntu) configured -- resuming normal operations
[Thu Feb 16 09:32:42.742657 2023] [core:notice] [pid 20500] AH00094: Command line: '/usr/sbin/apache2'
(END)

php -m
[PHP Modules]
calendar
Core
ctype
curl
date
dom
exif
FFI
fileinfo
filter
ftp
gettext
hash
iconv
json
ldap
libxml
mysqli
mysqlnd
openssl
pcntl
pcre
PDO
pdo_mysql
Phar
posix
readline
Reflection
session
shmop
SimpleXML
sockets
sodium
SPL
standard
sysvmsg
sysvsem
sysvshm
tokenizer
xml
xmlreader
xmlwriter
xsl
Zend OPcache
zip
zlib

[Zend Modules]
Zend OPcache


How did i install: git clone master > install php 7.4 and extensions > setup mysql > composer install > npm install > yarn install > completed install page on limesurvey without errors.

i started a debug session and here it is what i found:

"Error: Call to undefined function mb_ereg_replace() in /var/www/LimeSurvey/application/helpers/sanitize_helper.php:122
Stack trace:
#0 /var/www/LimeSurvey/application/models/Template.php(137): sanitize_filename()
#1 /var/www/LimeSurvey/application/models/Template.php(320): Template::templateNameFilter()
#2 /var/www/LimeSurvey/application/models/Template.php(508): Template::getTemplateConfiguration()
#3 /var/www/LimeSurvey/application/helpers/replacements_helper.php(125): Template::getInstance()
#4 /var/www/LimeSurvey/application/helpers/expressions/em_manager_helper.php(3340): templatereplace()
#5 /var/www/LimeSurvey/application/helpers/expressions/em_manager_helper.php(4543): LimeExpressionManager->setVariableAndTokenMappingsForExpressionManager()
#6 /var/www/LimeSurvey/application/controllers/SurveyAdministrationController.php(133): LimeExpressionManager::StartProcessingPage()
#7 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/actions/CInlineAction.php(49): SurveyAdministrationController->actionView()
#8 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/CController.php(308): CInlineAction->runWithParams()
#9 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/CController.php(286): CController->runAction()
#10 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/CController.php(265): CController->runActionWithFilters()
#11 /var/www/LimeSurvey/application/controllers/LSBaseController.php(145): CController->run()
#12 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/CWebApplication.php(282): LSBaseController->run()
#13 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/web/CWebApplication.php(141): CWebApplication->runController()
#14 /var/www/LimeSurvey/vendor/yiisoft/yii/framework/base/CApplication.php(185): CWebApplication->processRequest()
#15 /var/www/LimeSurvey/index.php(192): CApplication->run()
#16 {main}
REQUEST_URI=/index.php/surveyAdministration/view?surveyid=586152
HTTP_REFERER=http://localhost/index.php/surveyAdministration/listsurveys
---"

i found the solution mbstring module is not installed and limesurvey doesn't check on whether it is installed or not and it swallows the exception, another mistake so installing mbstring solves the problem.

apt install php7.4-mbstring