Block mode terminals are somewhat similar to the forms based UIs we later got like HTML.
The 3290 was like a 4 split tmux session, it is such a beautiful device (https://ifdesign.com/en/winner-ranking/project/ibm-3290-info...). Perfect keyboard, plasma contrast and the right text color for long sessions. My understanding is they outlived themselves with long service in air traffic control (supplementing vector/raster displays), financial markets, and software development. Once upon a time people seemed to really care about doing things well.
IBM's CICS has web support https://www.ibm.com/docs/en/cics-ts/5.6.0?topic=fundamentals...
It does turn out that 3270 streams and web forms are similar. Transmit a form, wait for the user to fill in the fields on the form, then receive the fields when the user submits it. It is how a mainframe in the 1970s/80s can support 100s of terminals, despite being small by modern standards.
That is a beautiful piece of industrial design.
IBM terminals were the original stateless clients. :)
I had a PS/2 Portable 70 for a while. It was a luggable Microchannel PC with a orange plasma display. Going through airports with it was a hassle as it didn't have batteries - I would have to find an outlet to power it on for airport security inspection.