Hello, this is Emily.
Can you clarify -
Are you trying to add a new school account to your computer, as a Windows log in using this new school account?
If so, First of all, you need to make sure your computer is running Windows Pro edition, If it is Home edition, then you won't be able to add a work account.
If you have Pro, to do so, go to Settings > Accounts > Access Work or School, click on Connect. (If you have anything listed there now, click on it, disconnect, restart the computer first).
Don't sign into your work email yet. Instead, click on "Join this device to Microsoft Entra ID". On the next step, you will be prompted to sign in, then you can sign in.
Once done, restart the computer and you can use "switch user" to sign in using the company email.