I would say that it is difficult to point a single (or a pair, or even 4) component that will make your bike more reliable.
I suggest you to check youtube videos from the United States of people doing mtb trails or rough roads on Walmart bicycle&similar cheap bicycle. You will be surprised at how much abuse they will get, and you may get some idea about what to upgrade (in short: possibly everything, practically almost nothing?). Even some cheap aluminium rims may take much more abuse than you expect, at least impact-wise (drops, steps, roots, rocks and so on...), although they will probably be off-centered after a few tens of kms and worn out after few thousands km).
Your bike is an entry-level, inexpensive all-rounder (knowing Decathlon&Walmart stuff, I guess your is a fairly priced bike, with a decent quality/price ratio, while Walmart bikes have often a very poor quality/price ratio ... and they are very cheap :) ! ).
Instead of going from tarmac to old glacier beds (what do you mean by failry rough ground? can you add a picture or a description?), I would suggest you trying your set-up step-wise, i.e. travelling further and on more complicated terrain. Keep in mind that if you have a major failure, you may end up walking home ...