As you may know using yay or makepkg to build and install AUR builds do not use the same keyring as pacman does, surprise surprise it uses your users keyring, but also GnuPG and its default keyserver with hkps:// protocol sks-keyservers still issue with that and you may want to use hkp:// instead:
make sure you do not have the file already!
ls: cannot access '/home/'username'/.gnupg/gpg.conf': No such file or directory
then touch the file and insert the hkp:// server-line:
echo keyserver hkp://pool.sks-keyservers.net > ~/.gnupg/gpg.conf
Now you should be able to get and add maintainer key to your local users keyring if needed.