Is it sufficing to have only one dmarc DNS record with name "_dmarc" and value "v=DMARC1;p=none" while I am having multiple subdomains, or i have to somehow manually add dmarc record for each subdomain or even use single wildcard type dmarc record for all subdomains?

ChatGPT says:
A single DMARC record at the organizational domain level (e.g., is sufficient to cover all subdomains. You don't need to create separate DMARC records for each subdomain or use a wildcard for all subdomains. The record with the name "_dmarc" and value "v=DMARC1; p=none" in the zone will apply to all subdomains by default, such as

However, if you want to have separate DMARC policies for specific subdomains, you can create individual DMARC records for those subdomains.