I strongly advise against writing down the master password itself. You would be turning a “something you know” factor into a “something you have” factor by doing that, which on its own is weaker than a properly random “something you know” factor and means you are unlikely to ever really be able to protect your password manager with MFA since most second factors are already “something you have”.
If really needed you could split it with Shamir’s Secret Sharing into 3+/n parts and give one each to a trusted party who wouldn’t be likely to collude with another to harm you. That sounds more complicated than it is, the parties could just be a biological family member, a friend, and a partner, for example. Usually people’s relationships of those kinds are such that there’s not really any risk of all three coming together to scheme against you in this way, but obviously make sure that’s the case in your situation for whoever you choose.
Just make sure whatever tool you use to split the secret is used entirely offline.