The point:

The Internet Corporation for Assigned Names and Numbers (ICANN) has officially reserved the top-level domain “.INTERNAL” for private-use applications.

• Interestingly but not surprisingly Google and some Google Cloud customers "has used .internal for years needed a private-use TLD to remove external dependencies and prevent collisions with delegated TLDs, due to the lack of an existing private-use name".

Benefits:

The reservation of “.internal” is finally providing a standardized and conflict-free namespace for network administrators and other users who require a domain name for internal or private purposes avoiding that uncoordinated use of private-use names could lead to DNS conflicts and vulnerabilities.

Credits and insights: ICANN reserves .internal for private use at the DNS level
If you like RFCs ;): Address Allocation for Private Internets