Here's a definition:
‘product with digital elements’ means a software or hardware product and its remote data processing solutions, including software or hardware components being placed on the market separately;
I don't think it's a stretch to say that such apps are components "placed on the market separately". In fact, I think it's exactly within the meaning. In any case, even if not, such loopholes are usually plugged by some of the vague, general obligations.
I don't think ADB installation is a loophole. Once you poke around in the insides of a device, you're generally on your own. I expect that devices are going to become more locked down before these regulations enter into force but only as far as absolutely necessary. Google doesn't want to lock out the next generation of devs. Unless or until there is some fuss about people doing something bad and this is declared a loophole.
The verification demand is for Google certified Android.
The OS or a phone both fit that definition.
An app fits the definition of a component.
Maybe you would have to argue that an app is not actually a component. But if it's a stand-alone thing, then why does it rely on an OS?
I think you can make a good argument that a phone without an OS is not a system. It's not capable of much. Maybe custom roms will remain an option.
Anyway, Google is not abusing that loophole. So, no problem. F-Droid encourages users to complain to EU lawmakers about Google being a meanie. Maybe the EU will close it anyway as part of future tech regulation.