I am trying to switch from Ubuntu to Windows, but when I use the sudo add-apt-repository ppa:nilarimogard/webupd8 command, I get this:

I am trying to switch from Ubuntu to Windows, but when I use the sudo add-apt-repository ppa:nilarimogard/webupd8 command, I get this:

When in doubt about any PPA, not just WebUpd8, it's always best to visit the official Launchpad Website for the PPA, and every reputable PPA has one of the form https://launchpad.net/{PPA Name} where PPA name will resemble the repository added in your apt.sources files. In short it's everything in the entry minus ppa. In WebUp8's case, it's WebUpd8 PPA Website.
Long Form For Illustration: https://launchpad.net/~nilarimogard/+archive/ubuntu/webupd8.
Once there for any repository,
Technical Details about this PPAChoose Your Ubuntu Version as a quick check. I've posted WebUp8's below:
As you can see from the cropped screenshot, version 23.04 isn't supported by this PPA, whether or not the version is EOL or not is now moot.
Just as a quick exercise, I Googled for woeusb and should the OP choose to follow whatever tutorial etc. was being used there is a PPA that supports Lunar (23.04). See Tomtomtom's WoeUSB PPA.
Long Form: https://launchpad.net/~tomtomtom/+archive/ubuntu/woeusb
which shows:
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