Anyway, I guess it all depends on what you call "reliability". What are your criterions? Any specific standard or guideline you may be referring to?
If I were to design a product which reliability/safety was important or even criticial, I would do as with any other components that I select: depending on its criticity in the system, I would ask for documentation and reports from the vendor asserting that some design steps have been taken and that some tests have been issued to ensure reliability according to some criterions. If the vendor is unable to provide this, then I won't be able to trust the component. That's as simple as that. So either I will look elsewhere, or, if I have no choice/really want to use this particular component, I will have its design analyzed and will have it tested properly so that I can have confidence and that I can myself prove it.
And, apart from the hardware, there's also the software. The "official" OS distributions for the RPi are OK, but I wouldn't know how fit they'd be for any critical application, and I guess no one, neither at RPi, or outside, would be able to guarantee that they are.
Of course this is all a matter of criticity. If you're mainly using an RPi as part of some "intelligent" display with no associated risk if it ever fails, then it's a whole different story. As others have said, you'll still have to consider the SD card issues (but doesn't the CM4 module embed Flash instead?)
And, of course, what I said potentially applies to any other SBC out there, except those that are specifically designed for industrial use AND are compliant with some relevant standards.