I believe this will be blocked by lack of official release for imagick that supports 8.0 (Imagick/imagick#358) unless you're going to build version off master yourself.

Not having an imagick release for PHP8 should not prevent at least a first version of a PHP8 image, imagick just might not work yet, but a new release of the extension will probably follow soon. And there are seemingly working versions of imagick for PHP8 out there: https://old.reddit.com/r/PHP/comments/k65h85/any_bumps_experienced_when_upgrading_to_php_80/gelz2m6/ - not sure if the same goes for ondrejs repository used by this image, would be worth a try at least.

Yes the current master of Imagick repository works fine, there's just no tagged stable release right now which means pecl can't be used.

The version in ondrej repository is last tagged stable with is NOT compatible with PHP 8.

For the v4 release, we are going to remove any extension that is not yet compatible with PHP 8 from the PHP 8 version (and we will document that in the README).
When the extensions are available, we will add those back.

Great! As soon as v4 comes out, I will test it with my projects.