The issue I had with COLORTERM is that not every program respects it. In fact, I've had this in my .bashrc for a while:
case $TERM in
linux | screen*)
unset COLORTERM
;;
*)
export COLORTERM=truecolor
;;
esac
A fork of terminfo may be needed if the description of modern terminal capabilities can't be added -- or if old and deprecated attributes repurposed for that job (like in your padding example): if you're automating the correction/creation of terminfos in ~/, IMHO, it may be better to piggyback on tic as much as possible.
Anyway, to backport modern terminal descriptions to legacy programs, creating correct binary terminfos in ~/.terminfo seems the best practice. You can also invent new TERM. When I wanted to have italics etc about everywhere, personally that's just what I did for sixel-tmux: https://github.com/csdvrx/sixel-tmux/?tab=readme-ov-file#ste... : just declare a new $TERM you know to be right, and use that in the apps that let you use a little logic in their configuration file
I do that in my .vimrc:
" If Vim doesn't know the escape codes to switch to italic
let &t_ZH="\e[3m"
let &t_ZR="\e[23m"
" Italics pseudo-auto toggle: force italics if we recognize it's supported from TERM
if match($TERM, "xterm-256color-italic")==0
highlight Comment cterm=italic
endif
Another idea: have you considered that the "program that would be run by .bashrc" to generate the "unambiguous 24-bit color capabilities" could set environment variables to communicate them? Like, if you can't stuff them in terminfo, stuff them in environment variables! Env var work well on Windows, and the configuration files of terminal programs could just use these when available to override.
It's be like adding friends to your proposed TERMVERSION: TERMSETF24 etc where you've have a finer control than COLORTERM
The other thing is that I like to close my laptop, reopen it the next day, and have access to the same remote buffers. (Maybe this is possible with TRAMP.)
Ultimately I just use emacs in tmux over ssh, with CLICOLOR defined appropriately, and this gets me 95% of what I want.
I wish I could get rid of those last <50ms of keypress latency. And variable-sized fonts for eglot inlay type annotations. They are quite distracting when they're the same size as the code.
This is partly due to the maintainer of ncurses being somewhat ... conservative and the new fangled terminal devs wanna move things fast.
As of Emacs 28. You still need the terminfo database in older versions of Emacs.
If unsetting COLORTERM fixes the display problem then it is a program issuing 24bit colors but the terminal (in your case screen) not understanding the escape sequences.