External Users Unable to Access Microsoft List Form

We have created a Microsoft List and are using the default Microsoft Lists Form for data entry / intake form.

Internal users can access the form URL and submit items successfully. However, external users are unable to access the form link, even though they have been granted Contribute permissions to the SharePoint list.

External users can:

• Access the list
• Create new items using the + New button
• Edit items based on their permissions

However, they cannot access the dedicated Microsoft Lists Form URL and getting following error.
This link is only available to internal users. This link is not available to you.

Our requirement is to allow external users to:

• Open the Microsoft Lists Form URL
• View the form
• Submit new items

without providing additional access beyond what is required for form submission, and without using Microsoft Forms.

Is guest/external user access to the Microsoft Lists Form experience supported? If so, what configuration or permissions are required to enable external users to access and submit items through the form URL?