I don't know why no one makes one - I've been thinking about this for maybe 35 years or so... Before there was a 'standing desk'.
Simple: it is a floor to ceiling post with a mount for the monitor and a separate one for the keyboard. The monitor adjusts to the desired height (standing or sitting) - there are many such monitor contraptions with a post, just not a _floor to ceiling_ post. The keyboard, likewise, slides up/down/out on an attached tray. The whole thing is minimal, takes up very little space, is easy to move, and makes a hella more sense than any desk.
In my case, I would want the keyboard to be pretty low and tilted in a way that minimizes wrist flex - perhaps a split keyboard to left and right of my waist.
Simple. But there is not one like that out there, and I have no workshop to hack up one. No 3-d printer, laser cutter, lathe, drill press. Table saw. Ehh. All that is in a different city. And in Manhattan, picking up 4 screws to fit the Vesa mount will probably cost $30 or more...
Ikea sells a post for $35.00 in the US, called ELVARI. It is not round, but it has a channel of some sort to hold shelves (as part of the closet system. That would work.
https://www.ikea.com/us/en/p/elvarli-post-white-40296170/
Amazon sells a round 28-mm spring-loaded post, MANFROTTO, for $65. It looks just sturdy enough to work, as long as the monitor is right on the post, without cantelevering.
https://www.amazon.com/Manfrotto-170-Spring-Loaded-Ceiling/dp/B001M4HUGA
There are many monitor arms that attach to a post, like this one:
https://www.amazon.com/VIVO-Universal-Monitor-Removable-MOUNT-POLE01A/dp/B083F3RPRK
Actually, there are a few things like this -- pretty much the entire workstation, just add a pole.
https://www.amazon.com/MonMount-Articulating-SSW001-Workstation-Keybord/dp/B01JGGPYTA