HI Puddles,
Yeah the UI was cleaned up, so you have to use the hot keys (or the pose menu) but it’s easy to remember CTRL C and CTRL V (Ctrl shift V for flipped)
Spikey has an extra add-on enabled called “Copy Attributes Menu” which is great for everything except animation.
(I’m just mentioning that in case you are wondering you can’t see that pop up anywhere)
With your particular issue, just make sure your mouse is over the 3d viewport when you are copying and pasting.
If it is over the timeline, it will copy the selected keyframes and paste them where you moved the playhead to.
I think that is what you may have done.