After I have installed TYPO3 on my local host this error occurs
The requested URL was not found on this server
I can show the login page of admin. After entering the credentials then occurs this error.
As written by Julian you need to make sure that there is the correct .htaccess file in your document root directory.
If the file is missing, you can find a sample file here:
/typo3/sysext/install/Resources/Private/FolderStructureTemplateFiles/root-htaccess
sometimes deleting .htaccess was the solution. (typo3 Install-Tool Environment offers to try repairing it. ) Rename your .htaccess, so you are able to compare differences later
This happens when upgrading from typo3 v10 to v11. The typo3v10 .htaccess is still used, and it does not have rewrites for /typo3/.
Remove the public/.htaccess file and run the install tool in /typo3/install.php and let the "Directory status" tool re-create it.