I think the main thing is now the app disappears if you click on a separate window. You used to be able to just change the window (ie. swapping between Chrome and Word) and Copilot would stay there. Now, changing the browser covers Copilot. Yes, you can drag each individual window to the side and do a split screen, but you have to do that for every other window. Before, it just happened.
I do like being able to move it anywhere on the screen, and that is something that should've been an option FOREVER ago. However, I think the sidebar was much better for switching back and forth between other windows.
Additionally, this new update kind of broke the Copilot key on my keyboard. I like being able to personalize what the key does now, but I liked it better before. The new version only opens the Copilot app and won't close it. The Preview could do both.
Lastly, my school has Copilot blocked, but not Chat GPT. The old one worked without the need for a VPN, but this new version requires me to turn on a VPN and then go to the app. I might as well just use Chat GPT 🤷♂️. Yes, that's my school's fault, not the new app's. Still, I used to use Copilot for convenience, and now it doesn't work quite as well for MY needs. And it doesn't really have to be, but I wish they let you choose between a few things, just IMO 🤷♂️🤷♂️.