When I try to unlink my Microsoft account from my minecraft PlayStation 4 by going into...

I need to unlink my PlayStation Network account from my old Microsoft account which I don’t remember, & link it to a new Microsoft account to play Minecraft

You can unlink the psn account however you CANT link a different one.

Note: Once a Microsoft account has been linked to a PlayStation® account, neither the Microsoft account nor the PlayStation™ Network account can be associated with a different account. 

If you choose to unlink accounts, then purchases will be returned to the account which made the purchase. Even after unlinking, Microsoft and PlayStation® accounts can only be re-linked to the original account.

This is coming right from the Minecraft website

https://help.minecraft.net/hc/en-us/articles/360037725571-Minecraft-for-PlayStation-TM-4-FAQ

That's really weird, since when you unlink a Minecraft/Microsoft account from a Playstation ID it can only be linked to the same Playstation ID.

Are you completely sure you are signed in with the correct Playstation ID and trying to login with the correct Minecraft/Microsoft Account?

Hello ,

Thank you for posting on the Xbox forums. We understand that you are unable to unlink your Microsoft account from your PlayStation account. There is

a support article on Minecraft's support website which explains more about linking and unlinking the accounts. There is a risk involved with unlinking the accounts. The article talks more about the risks of unlinking the accounts. If you would like to continue
to learn how to unlink the account, we suggest reaching out to
Mojang support and PlayStation support. Be sure to let us know the results!

I think I'll go with the option of creating a new Microsoft account for now, and so then whenever the unlink ability on minecraft is working I'll fix my brothers account. But I thank you for your great service.

Kind regards,

Fellow Gamer

Hello,

Please check out this page: Minecraft for PlayStation® FAQ – Home

It states:

Linking a Microsoft account to a Playstation® account

WARNING Once a Microsoft account has been linked to a PlayStation® account, neither the Microsoft account nor the PlayStation™ Network account can be associated with a different account. 

If you choose to unlink accounts, then purchases will be returned to the account which made the purchase. Even after unlinking, Microsoft and PlayStation® accounts can only be re-linked to the original account.

What happens when I unlink my Microsoft account?

IMPORTANT Once a Microsoft account has been linked to a PlayStation™ Network account, it cannot be unlinked without loss of access to entitlements and Minecoins on other platforms. 

According to this thread you can unlink the accounts: Minecraft PS4: Unlinking Microsoft Account - Microsoft Community

However, even if you unlink it, according to Mojang you can only Re-link it to the original account, you cannot link a different PlayStation account to the Microsoft account.

Thank you,

I am attempting to connect my microsoft account with my Ps4 account. My microsoft account is already connected to a Ps4 minecraft account. How do I find what Minecraft account is using my microsoft account and to disconnect it from it.

Even if you could disconnect it you wont be able to link a different Microsoft account.

Per https://help.minecraft.net/hc/en-us/articles/360037725571-Minecraft-for-PlayStation-4-FAQ

Note: Once a Microsoft account has been linked to a PlayStation® account, neither the Microsoft account nor the PlayStation™ Network account can be associated with a different account. 

If you choose to unlink accounts, then purchases will be returned to the account which made the purchase. Even after unlinking, Microsoft and PlayStation® accounts can only be re-linked to the original account.

Note: As of March 15, 2023, please DO NOT unlink your MSA from your PlayStation account via the in-game menu. You will be unable to link it back if you do so.

This is a restriction imposed by Sony.