Press the power button 5 times rapidly to enable "emergency mode" or whatever they call it. Biometric unlock will be disabled and you will have to enter your password/PIN to access the device again.
I don't think this is true. If you enable emergency mode video recording you have to enter your PIN to end the recording, but biometrics will still unlock the lockscreen. While the recording is going, hit the power button to activate the lockscreen, which will be unlockable with biometrics. You can also swipe up from the bottom (assuming gesture navigation) and switch to other apps. The device is not locked and not in lockdown mode while in emergency mode.
What you can do is press power and volume up to bring up the power menu, and then tap the "Lockdown" icon. That will lock the device and disable biometric authentication.
If you really, really want to lock it down, power the device down, or reboot it and don't log in. Android's disk encryption scheme uses your PIN/pattern/password ("lockscreen knowledge factor", or LSKF) along with keys stored in secure hardware to derive the disk encryption keys. It would make for a long post to go into all of the details, but given the hardware-enforced brute force mitigation,if the attacker gets a device in this state it's extremely difficult to decrypt any of the credential-encrypted data on the device without your LSKF. This is particularly true on devices that implement "StrongBox" (all Pixels, some Samsungs, some others). Android StrongBox moves some crucial functionality, including LSKF authentication and LSKF brute force resistance, into a separate hardened, lab-certified[*] security processor with its own internal storage, a "secure element".
Of course, note that appellate courts in the US have split on whether or not your LSKF can be compelled. Some have ruled that unless the PIN/pattern/password is itself incriminating, it's no different than compelling the combination to a safe, which has long been held to be constitutional.
[*] For anyone interested in the details, the required certification is Common Criteria EAL 4+ (5+ is recommended, and common, many devices meet 6+), using protection profile 0084 for the hardware and equivalent "high attack potential" evaluation for the software, plus AVA_VAN.5 penetration testing, all performed in a nationally-accredited security testing lab. While certification isn't a guarantee of security (nothing is), the required certification applies the highest level of scrutiny you can get for commercially-available devices. Apple also uses a similarly-certified SE in their devices, but it's not clear whether they use it for LSKF authentication, or whether they use their (uncertified) Secure Enclave.