My only previous Android experience was with Galaxy Ace years ago. And I absolutely hated it.
I'm confident that the experience on a Pixel will be fine, but is there anything I should be ready for?
You'll be getting vanilla Android (not Samsung's additions), and it's improved a great deal recently.
The Back button is in a different place and will screw with your muscle memory.
Hold down the power button to take a screenshot
Hold the home button, or enable "hey google" to start Assistant. It shits all over Siri from a great height and I use it all the time. Try things like "when I get to work tomorrow, remind me to call Jane" "3 minute 30 second timer" "next thursday, 3pm, dentists appointment" "what's 50pmh in metres per second?" "give me public transport directions to Trafalgar Square"
If you're stuck in fullscreen, swipe up to reveal the Home button
Hold the task switch button (bottom right, looks like a square) to enable split-screen view. Pressing Home while in split scren will temporarily replace the whole screen with the launcher. When you launch an app it will replace the previously "selected" half of the screen. You can resize the split by draggin the divider. Not all apps support split-screen (usually games).
Swipe down from the top for notifications and 6 quick settings icons. Swipe down to see more settings. In *this* view, tap the pencil and put your 6 most useful settings at the top. I have wifi, bluetooth, do not disturb, flashlight, airplane mode, rotation lock. Yours may differ. Tap a setting to turn it on/off. Hold it to get to the dedicated settings screen for that setting.
The homescreen launcher is much more customisable than Apple's. You can add widgets for things like calendar mini-view or weather forecast, or a fully-navigable menu of your browser bookmarks. Pinch-out on the launcher to edit the layout. Red-X-ing an app here just removes it from the homescreen. Tap the Apps button (centre bottom above Home) for a traditional list of all installed apps. Pinching-out and red-X-ing an app here uninstalls it.