Without using Grub can you switch operating systems with keyboard at startup?

[Ponce-De-Leon]

@SUPERFITTER

Is there a way to change to Legacy/MBR in the two Linux systems that I have?

Maybe this could help You:

[How To] Convert Zorin Grub EFI to MBR and reverse

There may be instances where a user must change their Zorin OS install from EFI to MBR (legacy) or MBR to EFI. Often, this may be in order to ensure a consistent booting experience if more than one OS is installed. You want all installed OS's to preferably use the same Boot format. To convert from MBR to EFI (Replace sdX with your actual drive I.D. like sda or nvme0n1...): sudo grub-install --boot-directory=/boot --bootloader-id=ubuntu --target=x86_64-efi --efi-directory=/boot/efi /dev/sdX …

@SUPERFITTER

If not how can I install them in a Legacy format?

There would be Rufus a good Tool because You can there choose between GPT and MBR. but Rufus is only working on Windows. So, You would need a Windows-PC for that. If You don't have one, maybe You can ask a Friend or Neighbor.