Conduit for low-voltage wire outdoors
Going back to finger safe voltages I use the contact limits in article 680 , 15v rms 30 for DC ,
However you are not talking about a body of water/pool
In chapter 9 of the NEC there are 2 tables 11a AC &amp;11b DC.
These show the classifications based on  the available voltage and current
Inherently limited power supplies 30-60v and under 100 va are class 2.
Class 2 do not propose a hazard and the wiring methods are just about whatever you want if your wiring is rated for running in walls no conduit is needed (even speaker wire run in walls needs to be listed for use in walls).
The wiring method used out side can be either pvc or emt. If you don’t think it’s going in the ground for 10-15 years I find emt less expensive because you don’t need a fitting you bend it. If you do use emt fittings They are reusable where once conduit is glued it is solid. So it is really up to what you want to use.