Best wiring setup for a 240V 30amp circuit (mix indoor/outdoor)? Sauna heater

I need to install a new 240V 30amp circuit for outdoor Sauna heater. Wires will come out Panel in my garage, into the attic, run 100ft to the back of the house and come down through the soffit inside a PVC conduit along the outdoor wall until its final box by the Sauna. Manufacturer recommends 8 gauge for this distance.

I installed circuits and wire before, I think I can do this, but I want to double click on the best cable/wire setup - Options in my mind:

1. Romex 8/2 - I see Romex in my attic, I don’t have a rodent problem apparently, but how does one migrate the Romex into the final conduit going outdoors through the soffit? I understand conduits need to be sealed on both ends.)
2. Metal Clad 8/2 – Would see to provide better protection in the attic, but again, can I just insert the metal conduit inside the final outdoor conduit?
3. THHN 8AWG wire going through PVC conduit all the way from the panel to the outdoor box - Seems straight forward but it will be a massive pain to install by myself.

Trying to balance adherence to code but not make it twice as complicated for me.

Thanks!!