xfce w/kernel 5.15.76.1
pamac 10.4.2-2
My Updates shows 1.1GB download size. I don’t know what half of them are for and if I need them or not. Seems like a lot of updates, and a blanket “apply” would just be asking for issues. ???
Am I missing something?
What is “Software mode”
You can also use pacman -Syyu on console to show which updates are coming to be downloaded.
Totally normal.
Most are just system updates.
No… but there might be known issues. Check: #announcements
What do you expect to miss?
Software mode just hides a bunch of packages, which are just for the system.
That might be about right, depending on whether it’s a new install and/or when you last updated.
You probably do. A lot of them will be system libraries, others are important system components, et al.
Updates in Manjaro are normally bundled together and issued in batches — barring urgent security fixes — approximately twice a month. They also always come with an announcement thread under the #announcements category, so best is to subscribe to notifications for that forum category. The announcement will commonly list the changes.
Updates to AUR packages are a different matter, but if it’s a new installation, then you won’t have any AUR packages installed yet. The AUR is the Arch User Repository and is not maintained by Manjaro. It is also not supported by Manjaro’s default configuration of pacman, although pamac does have support for it, if you enable that — it’s disabled by default.
It lists software titles, as opposed to individual packages.
Depending on which ISO was used, python2 packages might still be on the install and those where recently moved to AUR.
True, that. Therefore it is probably best to run the first update process from the command line with pacman only — this will skip the recently deprecated python2 packages — and to remove said packages from the system afterwards (unless one intends to keep them for whatever reason).
sudo pacman-mirrors -f5 && sudo pacman -Syyu
Subsequent updates can be handled with… 
pamac update
… or…
yay -Syu
Most of them should have a description telling what they are.
As pointed above, many are likely system related packages. But if they are to be updated, it is because those packages are either installed on your system, or (newly) required for other packages to be updated on your system. And considering partial updates are not supported, you should update everything list anyway.
The answer has already been given above. I just want to emphasize, always read the Stable Update Announcement Topic before updating, at least the first 2 posts by philm. It highlights major changes, if there are any issues and any manual steps that might be required.