Please help us help you and fill where relevant:
LimeSurvey version: LimeSurvey Community Edition Version 6.16.3+251215
Own server or LimeSurvey Cloud: Own
Survey theme/template: Not relevant
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I see:

500: Internal Server Error - Alias "application.controllers.admin.Update" is invalid. Make sure it points to an existing PHP file and the file is readable.

after wanting to update on my Limesurvey installation that I have just moved from one server to another, while also changing the URL. Do you know what is the matter here?

I checked: the file update.php is present in the folder application/controllers/admin
But it is spelled as update.php and not Update.php.

Thanks in advance,

Tammo

And no improvement after clearing the LimeSurvey cache and the browser cache.

same problem here, trying to upgrade to 7 beta.
500: Interner Serverfehler - LimeSurvey\Helpers\Update\Update_700::adjustShowCreateTable(): Argument #2 ($tableName) must be of type string, null given, called in /home/www/survey/application/helpers/update/updates/Update_700.php

Forgot the last line:

...on line 1035