The renderComponentIntoRoot component encountered an error while loading.

This matches a portal-side rendering/service issue rather than an application assignment configuration problem.

Relevant known cases with the same renderComponentIntoRoot error were caused by a recent deployment on the service side, and the mitigation was:

1. Do a hard refresh of the browser.
2. Clear the browser cache.
3. Retry the assignment page.

If the page loads again, assign the user or group from: Microsoft Entra admin center → Entra ID → Enterprise apps → All applications → select the app → Users and groups → Add user/group.

Expected result:

• The Add Assignment pane should load.
• The user or group search should return results.
• The assignment can then be completed by selecting the user/group, choosing a role, and selecting Assign.

If the page starts working but provisioning later shows assigned users as skipped, review the provisioning logs. A user marked as not effectively entitled can be fixed by unassigning the user or group from the app and then assigning it again.

Also note:

• Group assignment does not cascade to nested groups.
• Only users directly in the assigned group have access.

• Logic Apps Designer fails to load with "renderComponentIntoRoot" error across multiple users and environments - Microsoft Q&A
• Manage users and groups assignment to an application (portal)
• No users are being provisioned