Is it correct that the ONLY way to have Messages fully sync across Apple devices, is, to have iCloud turned on for Messages on all of them?

Currently, Messages basically does not work across my various laptops, iPhone, iPads.

When someone texts me (regardless of the mode of the text .. sms, etc) the message rather randomly appears on often just one of my devices, occasionally on more than one at the same time, or occasionally on more than one but only appearing with long periods of time between appearances (often days or weeks).

(I have been trying to work out the pattern, is it something like “the device that is turned on will only get the message” or “the device on cellular will only get it versus a device on WiFi” – or some pattern I can not determine.)

TBC normally and for years every single time I get (any sort of) message on Messages app – its message would pop up, instantly, all at once, on all devices.

I am attempting to not use iCloud and indeed I have turned off iCloud for Messages (as far as I know, on all of my devices). I did read somewhere that, indeed (and this is totally bizarre) iCloud is indeed the sync mechanism for Message app.

• I really can’t find any info on this. I would have thought there would be 10s of millions of people screaming about how Messages app essentially doesn’t work any more and messages don’t appear etc.
• Is it in fact the case that you must have iCloud turned on (what, on every device, or?) to make Messages app sync?