Not sure when this happened as I hadn't updated in a while. The checkbox column which was rather clear afaik with intent was swapped out for an action button type column on the other end of the window?
So now we have buttons that convey Install/Upgrade/Build, but the actual "checked"/enabled state is meant to be determined by the button being coloured green or not? That just feels very bad for UX and not intuitive at first glance.
I wasn't sure if it was just a theme colour for the button(since Manjaro likes to use green and by default it was all green Upgrade buttons in this column), perhaps you can communicate the two states better with different text or some inline icon to go with it if you insist on a button?
Any reason for repeating the button like this throughout a column vs just sticking to a more helpful column header? I get the buttons are providing some sort of context to what the column is intended for vs just a checkbox(though a column header should convey that just as well?), if there isn't multiple choice beyond binary state, what benefit is this actually adding? If you want some text, perhaps go with a tooltip?
IIRC, previously I could de-select all packages, and then select only the ones I want to update. Now I can only manually exclude packages(eg nvidia drivers when I've been away overseas for a few months and forgot to retain a kernel that didn't hit EOL which caused grief). I usually do this for AUR updates at times when I don't feel like downloading/building some rather large packages just because they had a small update.
Another UX issue with these action buttons, was with AUR. There is no install/upgrade difference, just build(for installing or upgrading), why? BTW, when the Pamac window is out of focus, the text on the action button if it's green goes black, changing back to white when the Pamac window is focused again, that sounds unintentional?(similar changes happen elsewhere(sidebar/headerbar)