Hal a few months ago I sent you the workshop manual for the BYD and I only really had a look at it now.
From what I've read there's nothing EV specific to any of the fluid changes.The method used in the factory manual is the same for all vehicles.
The coolant,brake fluid and gear oil l can be changed like a regular vehicle.The radiator coolant needs a small section of the subframe under the bumper unhlbolted but it's not impossible for a bloke with your experience.I'd say you'd probably get in there without taking the car apart.
Any mechanic that's worked on a few cars would have no problem doing the work if you didn't want to touch it yourself.The 40000km interval on the brake fluid seems excessive but I'm not an engineer.
It'd be interesting to see the ID4 Service Manual - without the bullshit certain dealers add.
Brake fluid on normal VAGs is after 3 years and then every 2 years with no kilometreage limits.
Coolant on normal VAGs is never - although there may be an exception for Alaska - can't remember for certain and can't be arsed opening the manual now. In any event it is possible to test coolant strength before / rather than replacing it.
Gearbox oil on normal VAGs is never. In fact if you drain through the drain plug alone you're only draining c.52% of the oil anyway.
I think Toyota impose kilometreage limits on everything, even brake fluid which degrades over time not usage so the EV manufacturers are probably copying that approach... I guess they're struggling to find stuff to charge ewes for in any event!