To my very surprise I wasn't able to find a decent DIN-rail mount for the RPI pico. So I made some changes to a mount I created for the original RPI a while ago.
Print it with the flat side facing down and use some support where necessary. And since the spring will be printed in an unfavorable orientation, make sure your settings prioritize layer adhesion. Tested positively with materials such as PETG and PC.
You'll also need 4x M2x6 screws for attaching the pico. Make sure the screw heads are small enough to not interfere with the electronic components.
The author marked this model as their own original creation.