TYPO3 v10.1.0 won't install - typo3

Question

I just wanted to install TYPO3 10.1.0, but the installation doesn't work.
At first, it throws an Server-500-error, without any php-errors.
After setting'displayErrors' => true I could see a detailed error message showing
Symfony\Component\DependencyInjection\Exception\InvalidArgumentException
The file "/var/www/html/typo3/public/typo3/sysext/core/Configuration//Services.yaml" does not contain valid YAML: Unexpected characters near "
I opend that file, and removed all comments inside it, and reloaded the install.php, which resolved that error, but another error was thrown, this time in my php-output:
NOTICE: PHP message: PHP Fatal error: Class TYPO3\CMS\Core\Mail\FileSpool contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Symfony\Component\Mailer\Transport\TransportInterface::__toString) in /var/www/html/typo3/public/typo3/sysext/core/Classes/Mail/FileSpool.php on line 38
After I added the __toString():string function in FileSpool.php, I get another error
NOTICE: PHP message: PHP Fatal error: Declaration of TYPO3\CMS\Core\Mail\Mailer::send(Symfony\Component\Mime\RawMessage $message, ?Symfony\Component\Mailer\SmtpEnvelope $envelope = NULL): void must be compatible with Symfony\Component\Mailer\MailerInterface::send(Symfony\Component\Mime\RawMessage $message, ?Symfony\Component\Mailer\Envelope $envelope = NULL): void in /var/www/html/typo3/public/typo3/sysext/core/Classes/Mail/Mailer.php on line 38
So, basically, the core/classes/Mail prevent me from installing TYPO3 10.1.0

Answer 1

This is a known problem caused by changes in Symfony version 4.4 components and is solved in current master or version 10.2.0 (release scheduled for tomorrow, December 3rd) see corresponding patch.
You currently have four options to circumvent this issue:
wait for the new release of tomorrow
use current master instead of 10.1
apply the patch to your installation
add the following lines to your composer.json
"conflict": {
"symfony/config": "~4.4.0",
"symfony/console": "~4.4.0",
"symfony/dependency-injection": "~4.4.0",
"symfony/expression-language": "~4.4.0",
"symfony/finder": "~4.4.0",
"symfony/mailer": "~4.4.0",
"symfony/mime": "~4.4.0",
"symfony/property-access": "~4.4.0",
"symfony/property-info": "~4.4.0",
"symfony/routing": "~4.4.0",
"symfony/yaml": "~4.4.0"
}