Did anyone address the low coolant being the result of a leak? I didn’t see the OP address it. Maybe one of the replies did.
Some background, to address leak issues.
I had a Toyota with a slow coolant leak. I monitored the level, and added coolant and distilled water(50/50) to keep it topped off. I noticed there was a direct correlation between the coolant level going down, and the normal engine temperature going up(duh).
I determined that I had a top end leak, or possibly a pinhole in the top end of the radiator.
Turned out to be an old hose.
If I was having the same issue, and my driving was mostly in a desert climate, I decided not to get myself in a Death Valley overheat situation from low coolant that might have even devolved into no coolant. Advice to OP, find the leak, and address it.

It’s a resurrection of a 3 year old post. But those are excellent suggestions and well worth noting.

If g40 was designed only for environmental reasons I’ll stick with g48, it’s most likely better at corrosion protection

Interesting. My copy of that document does not have the "Compatible with" column.
You're probably right, if your car called for G48 originally. The later spec shows "free of borat, 2- ethylhexanoic acid". Borat[e] (B) is one of the inhibitors listed in the earlier spec. 2- ethylhexanoic acid (2EHA) is harmful to nylon and silicone seals not designed to handle it, so probably best not to use the older formulation in cars made after April 2014.

We’re grinding this pretty hard. Maybe the best answer is use what your car came with until it becomes unavailable.

BTW-Thanks for the chemistry lesson. When I saw 2-ethylhexanoic acid I said to myself, “What the … is a fatty acid doing in anti-freeze?” I used to keep up with coolants in my Dupont Telar days, but haven’t dug deep for years, concentrating on lubricants instead.

This thread did go down the rabbit hole pretty quick... I would've said just use distilled water to top off. If your expansion tank is empty, you have other problems, but if it's only low then just distilled water should be fine.

And of course, change the coolant with the appropriate kind for your vehicle at the recommended interval, to make sure you have the correct concentration. But to just top off? Water.