Migration new paths - Error: Class not found

[cluster]

WHMCS: 7.10.3
PHP FPM 7.3
MariaDB 10.5.15
Debian 11

Migration Error
source system: Debian 10
target system: Debian 11

Due to an error on the host system, I have to move to a new system. I'm not able to use (update) whmcs 8.x beforehand.
The paths on the new system have changed, I have already updated the paths and storage paths, these work flawlessly. There are no further Apache or PHP error messages.
After the migration, everything works except for the following two things:

1. With many customers under clients, an error message appears when I click on the customer name
2. An error message appears for all support tickets

Oops!
Something went wrong and we couldn't process your request.

Clients (click clients name)

Error: Class 'Illuminate\Database\Eloquent\Relations\MorphTo' not found in /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/database/Eloquent/Model.php:836
Stack trace:
#0 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Model.php(0): Illuminate\Database\Eloquent\Model->morphTo()
#1 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/database/Eloquent/Model.php(2688): WHMCS\Payment\PayMethod\Model->payment()
#2 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/database/Eloquent/Model.php(2661): Illuminate\Database\Eloquent\Model->getRelationshipFromMethod('payment')
#3 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/database/Eloquent/Model.php(2605): Illuminate\Database\Eloquent\Model->getRelationValue('payment')
#4 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Model/AbstractModel.php(0): Illuminate\Database\Eloquent\Model->getAttribute('payment')
#5 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/database/Eloquent/Model.php(3397): WHMCS\Model\AbstractModel->getAttribute('payment')
#6 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Model.php(0): Illuminate\Database\Eloquent\Model->__get('payment')
#7 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Traits/TypeTrait.php(0): WHMCS\Payment\PayMethod\Model->getType()
#8 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Traits/TypeTrait.php(0): WHMCS\Payment\PayMethod\Model->isLocalCreditCard()
#9 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Collection.php(0): WHMCS\Payment\PayMethod\Model->isCreditCard()
#10 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/illuminate/support/Collection.php(203): WHMCS\Payment\PayMethod\Collection->WHMCS\Payment\PayMethod\{closure}(Object(WHMCS\Payment\PayMethod\Model), 0)
#11 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Payment/PayMethod/Collection.php(0): Illuminate\Support\Collection->filter(Object(Closure))
#12 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/includes/ccfunctions.php(0): WHMCS\Payment\PayMethod\Collection->creditCards()
#13 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/Client.php(0): getClientDefaultCardDetails(1707)
#14 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/admin35vwa2p8/clientssummary.php(0): WHMCS\Client->getDetails()
#15 {main}

 

Support Tickets

Error: Class 'HTMLPurifier_ChildDef_Required' not found in /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/ChildDef/Optional.php:10
Stack trace:
#0 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/composer/ClassLoader.php(444): include()
#1 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/home/users/whm...')
#2 [internal function]: Composer\Autoload\ClassLoader->loadClass('HTMLPurifier_Ch...')
#3 [internal function]: spl_autoload_call('HTMLPurifier_Ch...')
#4 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer.php(73): unserialize('O:27:"HTMLPurif...')
#5 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Decorator.php(81): HTMLPurifier_DefinitionCache_Serializer->get(Object(HTMLPurifier_Config))
#6 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Decorator/Cleanup.php(70): HTMLPurifier_DefinitionCache_Decorator->get(Object(HTMLPurifier_Config))
#7 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/Config.php(505): HTMLPurifier_DefinitionCache_Decorator_Cleanup->get(Object(HTMLPurifier_Config))
#8 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/Config.php(415): HTMLPurifier_Config->getDefinition('HTML', false, false)
#9 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier/Generator.php(74): HTMLPurifier_Config->getHTMLDefinition()
#10 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/ezyang/htmlpurifier/library/HTMLPurifier.php(158): HTMLPurifier_Generator->__construct(Object(HTMLPurifier_Config), Object(HTMLPurifier_Context))
#11 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/View/Markup/Markdown/Markdown.php(0): HTMLPurifier->purify('

Hello
<...')
#12 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/michelf/php-markdown/Michelf/Markdown.php(187): WHMCS\View\Markup\Markdown\Markdown->doHtmlPurifier('

Hello
<...')
#13 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/vendor/whmcs/whmcs-foundation/lib/View/Markup/Markup.php(0): Michelf\Markdown->transform('

Hello
<...')
#14 /home/users/whmcsdev/www/sub.mydomain.tld/htdocs/admin35vwa2p8/supporttickets.php(0): WHMCS\View\Markup\Markup->transform('Hello\r\n\r\nPour...', 'markdown')
#15 {main}

Unfortunately I can't get any further with this and need help

[cluster]

It seems some files were corrupted from FTP upload,

I have deleted everything and uploaded the original files explicitly in binary mode. After that it worked.