The above solution works. I found out that The Equivset will be installed if you update the file composer.local.json in the Mediawiki-Folder by this

{
"extra": {
    "merge-plugin": {
        "include": [
            "extensions/AbuseFilter/composer.json"
        ]
    }
}

Got that from the instruction:https://www.mediawiki.org/wiki/Extension:AbuseFilter .

Please aware of your previous contents in that file and adapt it consequently. After that, run the composer update or composer update --no-dev in the Mediawiki-Folder