Hi guys,
I installed SS version 4.11.2 via composer as suggested in the docs:
composer create-project silverstripe/installer
I created the .env file with all needed values and then run sake:
vendor/bin/sake dev/build
…
Database build completed!
Everything looks good:
[INFO]: — Building schema “admin” —
[INFO]: Creating new schema
[INFO]: Migrating new schema
[INFO]: Deleting temp schema
[INFO]: Total types: 59
[INFO]: Types built: 59
[INFO]: *CopyToStageInputType
[INFO]: *VersionedInputType
[INFO]: *FileFilterInput
[INFO]: *FileUsage
[INFO]: *PublicationNotice
[INFO]: *FileInput
[INFO]: *FolderInput
[INFO]: *File
[INFO]: *Folder
[INFO]: *DescendantFileCount
[INFO]: (… and 49 more)
[INFO]: Types deleted: 0
[INFO]: Built schema in 122ms.
[INFO]: — Building schema “default” —
[WARNING]: Schema default is empty. Skipping.
[INFO]: Built schema in 2ms.
But if I want to Login on /admin:
Service Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.
Tried reinstall severel times, but no success 
The frontend is working normal, standard theme is there and I can navigate through the page.
I run on PHP 8.1. Tried it also on 8.0, no success.
May anybody can help me?