gpg: no valid OpenPGP data found. (when adding the ppa)

[ghost]

gpg: keybox '/tmp/tmpev0jtpyr/pubring.gpg' created
gpg: /tmp/tmpev0jtpyr/trustdb.gpg: trustdb created
gpg: key 6CFDA3EBE08FDDE9: public key "Launchpad PPA for Luke Horwell" imported
gpg: Total number processed: 1
gpg: imported: 1
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
gpg: no valid OpenPGP data found.

[lah7]

Which distro & version are you using?

[lah7]

The last message looks like Debian 11 might have removed the apt-key method, but I don't actually know the successor command yet. If those commands above fail too, please take a look online to see what the alternate solution is:

Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).

I'm not on Debian to check the manual, but this might note how to do it:

man apt-key(8)

[ghost]

Is it supposed to be the packages with classic?
It does the same thing (as below) with all the classic packages (the formatting crossed it out because of the ~ ~)

After this operation, 449 kB of additional disk space will be used.
dpkg-deb: error: archive '/var/cache/apt/archives/libgtk-3-common_3.24.33-2classic22.04_all.deb' uses unknown compression for member 'control.tar.zst', giving up
dpkg: error processing archive /var/cache/apt/archives/libgtk-3-common_3.24.33-2classic22.04_all.deb (--unpack):
dpkg-deb --control subprocess returned error exit status 2
Errors were encountered while processing:
/var/cache/apt/archives/libgtk-3-common_3.24.33-2classic22.04_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

[lah7]

dpkg-deb: error: archive '/var/cache/apt/archives/libgtk-3-common_3.24.33-2classic22.04_all.deb' uses unknown compression for member 'control.tar.zst', giving up

Haven't seen that before, but it looks like Launchpad is providing control.tar.zst instead of the traditional control.tar.gz. At least that's the case for jammy (try switching the codename to impish or focal, though I don't know which GTK version Debian 11 uses).

According to this answer, Apt doesn't support zst compression, but Ubuntu's version does. Instead, what you could do is delete the repository and download each *_amd64.deb files into a folder and install manually with:

sudo apt install ./*.deb

[ghost]

The focal packages worked. But is there a way to make it so there isn't two title bars? Or is it just my theme that makes it looks like there's two?

[lah7]

That's a known bug: #32

Although you might be able to edit the theme so CSDs look like a toolbar.