@wrcombs My newbness is about to show again.
When I look at sources.list, some lines are preceded by a single hash plus a space (# ), some by a double hash plus a space (## ), and some with no hash at all.
Do I need to add any hashes? I ask b/c I added the lines without hashes, and this is the result
Hit:1 https://dl.winehq.org/wine-builds/ubuntu artful InRelease
Hit:2 http://archive.canonical.com/ubuntu bionic InRelease
Hit:3 https://dl.winehq.org/wine-builds/ubuntu xenial InRelease
Hit:4 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:5 https://repo.skype.com/deb stable InRelease
Hit:6 http://ca.archive.ubuntu.com/ubuntu bionic InRelease
Hit:7 http://ppa.launchpad.net/elementary-os/daily/ubuntu bionic InRelease
Hit:8 http://ca.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:9 http://ca.archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:10 http://ppa.launchpad.net/apt-fast/stable/ubuntu bionic InRelease
Hit:11 http://ppa.launchpad.net/atareao/atareao/ubuntu bionic InRelease
Hit:12 http://ppa.launchpad.net/linrunner/tlp/ubuntu bionic InRelease
Ign:13 http://ppa.launchpad.net/relan/exfat/ubuntu bionic InRelease
Hit:14 http://ppa.launchpad.net/ubuntuhandbook1/apps/ubuntu bionic InRelease
Err:15 http://ppa.launchpad.net/relan/exfat/ubuntu bionic Release 404 Not Found [IP: 91.189.95.83 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/relan/exfat/ubuntu bionic Release does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
sigh
Thank you for all your help; your google-fu is better than mine, even if it came to nothing. Looks like I'm finally forced to check out a wireless method this afternoon.