In my experience, the Canon RF 100mm f/2.8L Macro IS USM is tack sharp if SA is zeroed. For a budget, lightweight pick, the Canon RF 85mm f/2 Macro IS STM is solid.

Honestly I was so stressed about spending a fortune before my last trip. Getting the Canon RF 85mm f/2 Macro IS STM turned out to be a total win. It handled the humidity fine and didnt weigh down my pack like the bulky L glass would. TL;DR: Save some cash with the 85mm stm. It is light, cheap, and definitely sharp enough for that sensor.

Regarding what #1 said about the Canon RF 100mm f/2.8L Macro IS USM being sharp when you keep the SA ring at zero, I totally agree! I was so paranoid about my gear failing when I went to the tropics last year... I basically spent the whole first day checking my weather seals because the humidity was just insane! But honestly, once I got into the groove, the level of detail I got was just fantastic. It was amazing seeing everything so crisp! Since youre worried about weight tho, are you prioritizing that high 1.4x magnification for tiny insects, or is the physical size in your pack the biggest deal breaker? Also, what kind of lighting are you planning to use? Lugging a big flash through the jungle can be a total pain and might change how you want to balance everything!

Saving this whole thread. So much good info here you guys are awesome.