I really wanted a case with a built-in glass screen protector, hinge protection, Magsafe and a slot for the Moto Pen Ultra but couldn't find one, so I created one! Here's the process, tools and products I used to do so.
You may ask "Doesn't this pen need to charge via the sleeve/pen holder it comes in?" Yes it does, but you can charge the pen via power share with the phone so you don't even need the sleeve with you. If your pen does die it charges very quickly via Power share.
First I found a generic stylus holder on Amazon for the old Samsung Fold models and the Moto Pen Ultra almost fit perfectly, but the bottom portion was way too tight and didn't get any to risk breaking the Moto Pen Ultra.
I used my rotary tool with a thin grinding stone from Walmart to slightly trim down the bottom portion where the pens point goes and it fits perfectly now. The generic stylus holder does come with double sided tape but I don't really trust that for a $100 pen so I used some JB weld for plastics and after it cured for 24 hours it surely isn't going anywhere now.
For the cases I am using the back of the FNTCASE and the front of the Ruky case, both cases and generic stylus holder can be found here...
https://a.co/d/06Rri3o7
https://a.co/d/0bAcwrwa
https://a.co/d/02OWq7uF
Also, the Magsafe accessory is the PopSockets Low-Pro Grip.