[canistel]

An easier alternative is Ventoy. https://www.ventoy.net/en/index.html

Install Ventoy on a USB flash drive. Copy the ISO - copy as in cp. That's it.

You can add as many ISOs and select which one to boot with.

[7bit]

Ubuntu's Install medium supports secureboot. (As do many other Linux install mediums) I assume ventoy requires SB to be OFF, which does complicate things more, than just using Rufus.