Thank you for your replies!
Here are the steps I took:
I installed Mattermost on this new computer (Lenovo Ideapad) a few days ago. Upon realizing I cannot ctrl-c/v on it, I uninstalled and reinstalled it. When I did this, I realized it wasn’t really reinstalling a new program (no install wizard was appearing) it was clearly just opening a program that was already on the computer. No matter what I tried to delete, Mattermost files kept reappearing (that existed prior to my downloading the new file due to a file-restore). So I booted in safe mode and deleted every single Mattermost file I could find, and uninstalled it.
I re-downloaded it. When I tried to reinstall it, the install would just hang (green progress bar) at about 45% done. So I deleted that file and this time, I tried the MSI(beta) version. It installed normally - but the ctrl-c/v still doesn’t work. When I did a search for Mattermost, it looks like there is a Mattermost program file that keeps reappearing, and it dates back to November (whereas all other files are dated yesterday, the day when I did all of this).
By the way, the ctrl-c/v works for the Mattermost installed most of my other computers (my work Mac, a Lenovo 2-in1 tablet) but did not work on an old Dell running Ubuntu.
(Backstory: I restored the files for this new computer from an iDrive backup and I’m wondering if I mistakenly had it restore old program files. Since I’m also having problems on this new computer with it recognizing my password in SafeBoot I’m wondering if I should just do a factory reset and start over).
Sorry for the length. Hope the info is clear.