From someone a little extreme, in the hunt for boot/reboot seconds, here is what i have found so far.
These tweaks is not for everyone, if you are not comfortable doing the things below, please dont…
Bios:
Disabled cpu virtualization in bios, as i dont use virtual machines, gained as far as i remember about 4 seconds in total boot time.
*Edit 8/9-24- Have to correct the statement above, turning virtualization off do not save time, the time i found was from uninstalling KVM (Kernel-based Virtual Machine).
Fedora:
Disabled obvious services i do not need/want, then searched information about what different services do, and have along the way disabled more, so that i now disable 20 services, and have not had any issues on F39 or F40. Its a good idea to keep a log of the services you disable, so you are able to turn them back on if you find issues.
Uninstalled plymouth and removed rhgb quiet in /etc/default/grub, as i prefer to visually follow the boot process.
Dont remember the total time i saved on boot/reboot (was using F37 or F38 at the time), but in my book it is quite a lot, and absolutely worth it, but it depends on what services you need, if you need virtualisation, or prefer to boot with plymouth enabled.
Other than these tweaks i have hidden the grub menu (menu_auto_hide=1): https://discussion.fedoraproject.org/t/make-grub-hidden-again/98688 - for reboot speedup and convenience.
Last thing i want to mention is systemctl soft-reboot, which i have been using for over 6 months now, and the reboot speed is brilliant. I use it if i have updates without a new kernel (use terminal for system updates), and have yet to find any issues using it. Made a keyboard shortcut and a terminal alias command, to be able to use it quickly.
Made a setup-script so that these changes is easily applied (disabling services, remove plymouth, hide grub menu and more), if i want to re-install Fedora.