Coming up on hour 2 to beat this thing... but one thing eludes me... how the heck do I jump off a tentacle before I get body-slammed? I've tried spamming Enter, Space, r/l clicking to no avail.

When I did it he jumped off automatically when the QTE was over.

I;m playing with the gamepad and at the last sec it tells me to press the A button.
So look at near the bottom where geralt is, the QTE prompt should show up there.

Finally.

It was the space bar btw - hard to notice it flash at the last second as you get whipped around.

You have an option to disable difficult QTEs. See if that helps.

With a keyboard, the key you need to press to jump off is spacebar. Just spam it after you hack at the tentacle (the part where you rapid fire left click) and you should be fine

You only need to hit it one time when the prompt pops on screen. Pretty simple if you catch it. I only noticed it the second time I was riding the tentacle.