Hello Fredrik Bålstedt,
Thank you for posting your question in the Microsoft Q&A Community.
From my understanding, guest users cannot access an application due to approval issues.
Please be informed that this results from the User consent for application settings in your tenant being set to No.
There are a few ways to resolve this;
Firstly, Since you would like to approve permissions to the application without the need to always request consent, Admin can grant tenant-wide admin consent in the Enterprise App Pane.
Follow the link for more information. https://learn.microsoft.com/en-us/entra/identity/enterprise-apps/grant-admin-consent?pivots=portal#grant-tenant-wide-admin-consent-in-enterprise-apps-pane
Secondly, you can change the User consent setting to Allow user Consent for app from verified publishers by going to the User setting under Enterprise Application blade
Lastly, Under the Admin consent settings, you can allow users to request admin consent to apps and you can add the reviewers of this consent under the Users and Groups tabs as shown in the image below.
With this in place, the admin will approve access to the application.
Let me know if further assistance is needed.
Babafemi