Thank you for posting your query on Microsoft Q&A, from above description I could understand that you are planning to enable B2B collaboration between GCC high and a commercial tenant.
*Please do correct me if this is not the ask by responding in the comments section.*I have been through the settings you mentioned in the query above but did not find the following.
- Kindly validate if Microsoft cloud settings is enabled, Microsoft cloud settings allow you to collaborate with organizations from different Microsoft clouds such as:
Microsoft Azure commercial cloud and Microsoft Azure Government
Microsoft Azure commercial cloud and Microsoft Azure operated by 21Vianet (operated by 21Vianet)
If you don't have any further queries and the suggested answer is as per your business need, please "Accept the answer", This will help us and others in the community as well.
Thanks,
Akshay Kaushik