If you'd like to use the latest eglot without having to rebuild emacs from source or depend on 29 just yet:
(use-package eglot
:straight (eglot :type git
:host nil
:repo "git://git.sv.gnu.org/emacs.git"
:files ("lisp/progmodes/eglot.el"))
... )
This will fetch it from the git repo directly and straight will take care of the rest.
Cheers :)