Hello @Chirag Darji ,
Thank you for posting here.
Is your AD forest a single forest with single domain with only two DCs (a PDC and a RODC)? If so, RODCs cannot act as operations master role holders when PDC server is down.
From the following link, we can see:

For more information, we can refer to link below.
Planning Operations Master Role Placement
https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/plan/planning-operations-master-role-placement
If you only have one RWDC (PDC) and it is down due to some reason, I suggest you can:
1.Try to fix the issue of the PDC.
2.Ad another RWDC in the same domain and transfer FSMO roles to this new RWDC.
Hope the information above is helpful.
Should you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou
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Some good info here on RODCs
https://techcommunity.microsoft.com/t5/ask-the-directory-services-team/understanding-8220-read-only-domain-controller-8221/ba-p/395031