You will still be required to hand it over, or sit in jail while your confiscated, inventoried equipment is processed by forensics. If I want to be subpoena proof, I’d host the subject system outside the jurisdiction with an org having no connection or nexus in the adversary jurisdiction. Admittedly, this is up to your threat model. Do you want to know, but still be legally required to provide access? Or do you want to be out of reach entirely? The answer to that will guide your implementation and operating model in this context.

I don't mind being warranted, if they come to the door with warrant I will give them my boring, pedestrian inbox

but I do mind my data being drag-netted, or hoovered up by scummy big tech and then sold on

(whether that's for slop training, ads, anything really)

Why do you mind that? Your life is exactly the same one way or another. Principles, I guess, but it looks to me its just for the sake of it. For me, time is precious, all I need is data safety so I backup stuff offline constantly.