I honestly wouldn’t really say they are beginner dogs at all because if you don’t know what you are doing, they can get into serious trouble. They’re great dogs but not for everybody.
They’re often prone to sound and just general environment sensitivity and notice everything as well all of which can easily turn into reactivity if you’re not careful and they’re very quick dogs which means they will react quick too.
All of that is great on a farm (they need to be able to notice the slightest changes in their environment or know that that sheep is going to go there and react accordingly) but not so much as a pet. They can be very intense dogs too especially with the “eye” and can be prone to OCD and anxiety.
Also, a walk is nothing for a Border Collie. They need mostly mental stimulation tbh due to their smarts as well as a job to do. Whether that’s just trick training and obedience or wearing a backpack around, puzzle games, nose work, or whether that’s an actual sport like disc or agility or flyball they need
something. And they need physical exercise too like lots of running. Not just a a walk around the block.
Due to their smarts as well, its very easily to accidentally train bad behavior in even if you just make the mistake once and then very hard to undo. They will train you if you are not careful.
Can be reserved with strangers as well or even aggressive if you’re not careful and same for other animals.
However, all of that said, they are FANTASTIC dogs and if you can handle them, I would recommend them for sure. For me, I know I couldn’t so I haven’t gotten one. However, there are some lines, especially show lines, that are a lot calmer, some even veritable couch potatoes LOL, and those might be better for beginners than, say, a working cow dog or a sport line (mostly crazy and hyper

do not get one), but they’re also not really “Border Collies” IMO. But I do understand the need/market for them now and I’d get one of those if anything but yeah.
They’re great dogs and they’re not super difficult as long as you provide enough exercise and mental stimulation and find a good trainer if you’re not knowledgeable (or even if you are) but I still wouldn’t say they’re beginner dogs.
Especially considering some breeds, like the retrievers, might just be extremely hyper if they’re not trained/exercised but they’re still relatively stable dogs and not really dangerous if they don’t get it whereas a Border Collie can very easily turn unstable and neurotic without it. But often even with enough work and exercise they can be because they just live for the job.
But it is very possible (and necessary for your sanity

) to teach them an “off switch” for inside the house but even that depends on the dog. With some it’s pretty natural but with others, it’s very difficult to teach. So I’d try to find one who’s parents are calmer if you want.
But to say they’re beginners is misleading and possibly dangerous UNLESS someone is willing to put in the time and research and train properly.