Turning File Vault on, and instantly upgrading to macOS Big Sur is not a problem?

I just got a new MacBook Pro 16 inch from the IT department, and after I turned on the machine, it asked me for a series of set up questions.

One of them is File Vault, so I answered "Yes". But it takes no time to set it up, as opposed to some online page stating it took forever.

But there is another post stating it will be encrypting silently in the background?

So while I am not sure if it really should take some time or is it instant, due to my work, I need to immediately upgrade to macOS Big Sur from Catalina.

So will it be alright while File Vault is encrypting files in the background and the OS is being upgraded? I take it the upgrade process should be smart enough to handle that.

I manage macbook pros all day everyday, and I absolutely do not recommend upgrading OS's in the middle of encryption.

That said, since it's a new machine with no files on it, and since you enabled it already, chances are that by the time I post this, the encryption process is complete (only if it has been connected to power! otherwise the encryption pauses until it IS connected to a power source).

If it has a T2 chip it's encrypted already with blank password. Turning FileVault on just sets a different password and is instant.

From this Apple PDF : Apple T2 Security Chip Security Overview

If FileVault isn’t enabled on a Mac with the T2 chip during the initial Setup Assistant process, the volume is still encrypted, but the volume key is protected only by the hardware UID in the Secure Enclave. If FileVault is enabled later—a process that is immediate since the data was already encrypted—an anti-replay mechanism prevents the old key (based on hardware UID only) from being used to decrypt the volume. The volume is then protected by a combination of the user password with the hardware UID as previously described.

The links in the question apply to older models.