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Hello @thomas-kl1,

Thank you for the report and collaboration!

Verified this on 2.4-develop.
In app/code/Magento/Backend/App/Area/FrontNameResolver::isHostBackend() we do not need to pass the scope in $this->scopeConfig->getValue(), as Admin URL is global, instead default scope should be used.
Hence this issue can be confirmed.

Thank you.

✅ Jira issue https://jira.corp.adobe.com/browse/AC-11736 is successfully created for this GitHub issue.

✅ Confirmed by @engcom-November. Thank you for verifying the issue.
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