What happens if you forget your master password?
The short answer
With most password managers nobody, not even the company, can recover a forgotten master password. That is the flip side of zero-knowledge security. So set up a safety net in advance. A printed recovery code, emergency access for someone you trust, or 1Password's family recovery.
In detail
Zero-knowledge literally means the provider knows nothing. Your vault is encrypted with your master password, and without it there is no back door. That is exactly what you want against hackers, but it also means a forgotten master password can, in the worst case, mean a lost vault.
Every serious manager therefore offers safety nets you must set up beforehand. Bitwarden and Proton Pass give you a recovery code to print once and store somewhere safe. Bitwarden Premium has emergency access, where a trusted person can request access to your vault after a waiting period. With 1Password Families, a family member can recover your account, and you also get the printable Emergency Kit.
If you use a manager, do this today. Print the recovery code or Emergency Kit, keep it with your passport, and tell one trusted person where it is. Five minutes of work, and the forgotten-master-password scenario stops being a disaster.