Tested in my project running on Symfony 5.4, PHP 8.1 at it works.
Dropped SF3 because the code already contains classes from Twig 3 which is not supported in SF3.
From SF4 required PHP is >=7.1.3, so I see no reason to keep support for 5.6 in composer.json.
Bellow SF4 version v4.1.0 can be used, from SF4 this one should work.
I think you should make this version 5 since there are major changes in compatibility.
Tested in my project running on Symfony 5.4, PHP 8.1 at it works.
Dropped SF3 because the code already contains classes from Twig 3 which is not supported in SF3. From SF4 required PHP is >=7.1.3, so I see no reason to keep support for 5.6 in composer.json.
Bellow SF4 version v4.1.0 can be used, from SF4 this one should work. I think you should make this version 5 since there are major changes in compatibility.