Installing Ubuntu 20.04 next to macOS Mojave on a 2014 MacBook Pro. Can I then delete macOS in GParter and add its Ubuntu partition?

Question

macOS

I am planning the following:

1. From under MacOS, cut off a 40gb partition using Disk Utility
   
2. Reboot mac with alt pressed, boot from usb ubuntu and install it on 40gb partition
   
3. Sit on Ubuntu
   
4. If you don't like it, boot into macOS and in Disk Utility just delete the 40gb partition and return it to macOS
   
5. If you like, boot into Ubuntu and delete the macOS partition in GParter and add it to Ubuntu
   

Are there pitfalls in steps 4 and 5? Is everything so simple? After installing Ubuntu, will it change the Mac bootloader to grub? Step 4 will return everything as it was before these machinations?

ps The VirtualBOX and USB Live options are not suitable for my purposes.

Answer 1

You can! (then just delete the partition of one of the two systems
(if you want to restore macOS, you need a flash drive and https://support.apple.com/macos )