I have done a very deep dive on this, and essentially the issue is that the kernel of the ROM my phone runs (and by extension, many other ROMs) doesn't contain the cifs.ko module. This is the module that you need to mount a share to the filesystem natively.
From here I see basically 2/3 options:
I can install a custom ROM like lineage that has the cifs.ko module
I can make my own module (not going to happen)
I can wait for someone else to do it.
I've gone for the 4th secret option, use Windows.
Honestly, it's been an interesting and thought provoking couple of weeks, and I've learned a lot, but I don't want to install a custom ROM on my phone. I'll consider it on my Fire if and when it gets rooted, but essentially, all I'm missing now is that sweet spot where ROMs are large enough to take up a lot of space en mass, yet old enough to be loadable over an Internet share, so PS1 ish.
In the meantime, I essentially traded a Fire HD 10 2021 for a Surface Go 2, and it's so much easier to set up the Windows device, I can't see myself going back. I still have the Fire HD 8, but idk, it's just the worst of all worlds now between my phone and the Go.
Let me know if you have any questions I can answer