Can I use shapeoko xxl as a jointer to flatten wood, remove twists, etc.?
The trick would be securely holding the wood without inducing warp that would return after flattening.
Would be relatively long to flatten compared to jointer and would be only for short narrow planks. You would also need to hold the planks flat if they were crooked.
Yes. You could use it similar to a the way one would use a router table for edge jointing. If you’re more specific, someone can provide more details.
I have used it to flatten end grain cutting boards. If you are not perfectly trammed, you will get some lines/grooves, but it was good enough for me to get a reference to put through the planer then flip and plane off any lines/grooves.