When you opt for Advanced Installation for 12.1.0.2 Grid installation on RHEL 8 operating system and when you do designate the private interfaces subnets either as "ASM" or as "ASM & Private". You will get [INS-41210] one of the available network subnets is marked for use by ASM.
Solution:
Just use "Private" rather than "ASM & Private" for both the private interface subnets and leave the last one as Public for the Public interface subnet.
