Based on your and my comment:
- Comment Question: is those subscriptions on same Azure AD tenants?
- Comment Answer: No. Thinks of all together different Business Org. Different subscription
My Answer to your question is:
Managed identities exist in the Azure AD tenant as service principals. It is therefore can only be assigned access to any subscription connected to that Azure AD tenant.
So in short, if the subscriptions are connected to different Azure AD tenants, it wont be possible to achieve what you are asking about as far as I know.
EDIT
In addition to your comment
Comment: Can managed identity be used if all tenants were in same subscription?
My answer is: Each subscription can only belong to one tenant. please check Microsoft doc https://learn.microsoft.com/en-us/microsoft-365/enterprise/subscriptions-licenses-accounts-and-tenants-for-microsoft-cloud-offerings?view=o365-worldwide
Note: if this is feasible by one or other way and there are answer that can show the opposite of my experience and knowledge, I will be glad to know that as well.