** Emacs is now capable of editing files with very long lines.
The display of long lines has been optimized, and Emacs should no
longer choke when a buffer on display contains long lines. The
variable 'long-line-threshold' controls whether and when these display
optimizations are in effect.
A companion variable 'large-hscroll-threshold' controls when another
set of display optimizations are in effect, which are aimed
specifically at speeding up display of long lines that are truncated
on display.
Long line handling has greatly improved in emacs-29. Multi-megabyte lines are not a problem anymore.