Ender 3: Bowden Tube Popping Out
Verify that the Bowden Tube Fitting has a Lock Clip attached.
You might be able to secure the tubing with a Zip Tie and a Stud Ring Terminal from a local hardware store. The appropriate size might range from m4 to m6.
Consider using a Mod.
Bowden PTFE tube Clamp
Ender 3 Bowden Tube Lock Zip Ties
3D printed bowden tube coupling
Ender & CR10 Filament Extruder Block with Threaded Coupler and Nut