I don’t see that relatively new addition to the messages as a bug or problem. It clearly tells the user which kernel is booting just after the grub menu is passed (whether the grub menu is hidden or displayed) and only appears for a very few seconds.
The message does not come from grub2.cfg. It is coded into grub2 inself, and you would need to recompile it from source to modify this.
If the messages appears, depends on whether you let the boot menu time out or select the current entry by hitting the return key.
Supposedly you can disable the grub2 boot menu, and in this case the message should not appear, according to the source code.
The commit message reads:
Author: Hans de Goede <email@example.com>
Date: Fri Jan 28 11:30:32 2022 +0100
normal/menu: Don't show "Booting `%s'" msg when auto-booting with TIMEOUT_STYLE_HIDDEN
When the user has asked the menu code to be hidden/quiet and the current
entry is being autobooted because the timeout has expired don't show
the "Booting `%s'" msg.
This is necessary to let flicker-free boots really be flicker free,
otherwise the "Booting `%s'" msg will kick the EFI fb into text mode
and show the msg, breaking the flicker-free experience.
Signed-off-by: Hans de Goede <firstname.lastname@example.org>