Functional prototype of 20mm x ~7mm PCB button. Button feedback is nice (sound + feel).

button type 6x6mm tactile switch (4.3mm height, 4.5mm might also work)
Print faces down. No supports. PLA/PETG tested. Use <=0.2mm thickness.

Layers needs to be strong, due you have to use REALLY much power to push cap on base (Sounds like button crunched broken, but it will not, at least mine).
If fitting feels too tight, adjust sketch on FreeCAD (Highlighted measure on attached image; add for example "-0.1mm" at end of formula).
FreeCAD model is preliminary, (modeled bad, and unused variables,I need redesign with better variable settings)
There is also slotted version, Enable setting "Supressed" to false, on FreeCAD Boolean opertion. On PLA slotted version broke.