I'm not sure this is true. It's a reasonable concern, but in practice I don't think it turns out this way.
Two points, entirely anecdotal:
1) A few years back, I sort of "restarted" as a Salesforce developer. I had well over a decade of web dev experience, but I was new to SF. Everything about it was unique to this environment. I worked in an office, but my boss worked from home (ironically enough). So I was effectively remote working with him from the get go, and I found it worked really well.
2) My kids learn a remarkable amount of stuff on their own: Minecraft, Roblox, Scratch. All these programming environments that they've become really proficient at, and entirely on their own. This is effectively remote work. There was no one holding their hand.
I think the bigger issue is going to be getting employers to trust that the junior is working well. In truth, most junior employees probably don't have the maturity and discipline to be productive remotely. I certainly wouldn't have back when I was 18-22. I would have taken every chance I could to goof off, and not even considered whether that was a problem.
That kind work ethic (i.e. a bad one) tends to get beaten out of you pretty quick in the early days of a professional career. But a lot (most?) people fresh out of college still have that student mentality of viewing "adults" (bosses, teachers, parents) as authority figures to be rebelled against to some extent. I wouldn't trust someone with that mentality to be productive unsupervised.
The natural counter point is that if you can't be trusted, you shouldn't be hired. But I think that's a mistake. There's an awful lot of talented and smart young people who need a break or two in order to develop the appropriate work ethic and achieve their potential.
All of which is to say, I share your concern about opportunities for junior developers (and junior workers in general), but for different reasons.