My vote goes to soil toxicity.

Most carnivorous plants evolved carnivory in response to poor soil nutrient availability. Along the way, they also came to be very sensitive to soil nutrient levels (too many nutrients in the soil can actually be toxic to them).

For that reason, most carnivorous plants, especially species that naturally grow in bogs (like Sarracenia), should be grown in very nutrient-poor soil, and watered with very pure water. 50/50 pure peat and quartz sand (not builders sand, etc; that often has a lot of minerals) or perlite is usually the easiest and most effective. And the water you use should be very very clean; when I grew carnivores (I had close to 1000 of them), I used a reverse osmosis unit, getting the water to 0tds (zero total dissolved solids, essentially distilled water).

Soil from around your house probably contains too many nutrients, and if you're watering with tap water, that only compounds the issue (especially chlorinated water).

Carnivorous plants can be very finicky and, as a result, are kind of niche. SUPER cool plants, though, and they're highly rewarding when you get it right.

OruxMaps is the best I've ever found (and it's free). Been using it for nearly 15 years, still getting updated. Extremely flexible and powerful, though navigating the app itself sometimes feels kind of obtuse.

OpenAndroMaps for getting nice maps to use with it.

Mongo isn't appalled.

Absolutely loving the series!

It's very easy. It can be done through calibre, yes, although I prefer self-hosting a library that the kobo syncs to. I've used Calibre-Web, and recently moved to BookLore (NOTE: if anyone from the future reads this, the Booklore dev had a very public crashing-out (reddit link); the new one seems like it's gonna be Grimmory), and the latter is really, really nice so far. I have three people set up with their own accounts on BookLore, and we share one general library, but each person also gets their own personal library to do with as they please, and each person can choose what they want on their kobo, and it all syncs just by hitting the sync button on the kobo (you point the kobo to your own "store" instead of the kobo store). If you want to keep the stock store with the ability to also load "alternatively sourced" books, that's also easy with OPDS, also supported (very well) in BookLore.

Kobo can also be pretty customizable too, for what it's worth. KOReader is highly customizable, but if that's not your jam, there's also kobopatch which can change the default OS to some degree. Also NickleMenu, NickleClock, etc. There's plenty available to tune a kobo, imo, and I'm someone that's generally very "tinkery" with stuff.