It literally takes 20% of the CPU of my i5-10400 randomly, and even 40%

The app

just use dd or Popsicle (popsicle has a native gtk gui) or Ventoy

I stopped using programs like etcher for flashing iso’s after i found out you can just run

cp /path/to/your/file/example.iso /dev/[insert device here]

For example

sudo cp ./Downloads/archlinux-2023-09-01.iso /dev/sdb

I love it because it just works on any linux machine, always. Of course, this is maybe not fit for your usecase.

You can also use dd, tee or even echo, the archwiki has a good section on flashing iso’s.

If you have the iso image, you can write it with the command dd to your stick / sdcard

does Ventoy work for your use case ? write the ventoy image onto the usb, then you can copy/paste .iso files onto it without formatting. real neat for booting different systems from a single usb