This is FLOSS: Free Libre Open Source Software, so:
if you’re a developer, you can do anything and just fork the source and set the default the way you want it to be and send a patch upstream.
if you’re not a developer, you’re dependant on the developer’s default (I.E. what most people want) and the only thing you can do is to go to the Thunar Bug page and raise a “feature request” that you want to have a new parameter to be able to change the default from #2 to #1. Depending on how many people upvote your feature request, it might me implemented or not…
I’ve marked the below answer as the solution to your question as it is by far the best answer you’ll get.
However, if you disagree with my choice, please feel free to take any other answer as the solution to your question or even remove the solution altogether: You are in control! (If you disagree with my choice, just send me a personal message and explain why I shouldn’t have done this or or if you agree)
P.S. In the future, please don’t forget to come back and click the 3 dots below the answer to mark a solution like this below the answer that helped you most:
so that the next person that has the exact same problem you just had will benefit from your post as well as your question will now be in the “solved” status.