If you close your eyes the face id won't work. I suppose the police could force you to open your eyes somehow but if they are going to do that they can force you to put your pin in too.
they don't have to torture you. They can pressure you in all kinds of ways. Even mere threat of locking you up and throwing away the key would get you to unlock your phone.
Psychologically, the best chance they have is convincing you to unlock it. However, a privacy focused user that takes the initiave to use a custom rom like grapheneOS and not use any services that will compromise your data if requested might as well not have their phone exist at all. If they don't want you in, you are not getting in.
That's not really the point. Innocent people have the right to not have their things searched and dug through. Every person has some level of privacy that they want to keep. Let's say you have nudes from your significant other and yourself all over your phone. You don't want that information being seen by anyone else because it was meant for you and you alone. I guarantee your partner doesn't want random people seeing them either.
It is well known there have been bad actors in the IT and police that will make copies of that for their own personal use while they are supposed to be doing something else. Would really want to risk that?
Let me clarify, legally speaking you do, but I am not arguing that. Practically speaking, that device can become fort Knox with a properly configured phone. Use a custom android ROM like grapheneOS and not use any services that can/will give you access to the content on your phone and that phone is practically useless to them. Even with a warrant, you aren't beating today's privacy and security practices without a major security flaw. If a person doesn't want you to know what they have, they don't have to give you anything.
Will their be consequences? Probably, but that may or may not be worth it to you if you are a privacy activist who doesn't want to be incriminated on a legally but not moral basis. Or you could be a criminal with something you really want to hide. Doesn't really matter in the end.