I second zdanko’s recommendation of Gimp: it’s extremely powerful, versatile, and extensible software. It is cost free, open source, works offline, and runs well on both Microsoft Windows and on Linux (it also currently runs on Mac OS, but they’re having trouble finding developers who use Macs to work on the program, so I wouldn’t expect Mac to be supported forever unless that changes). It does have a steep learning curve, but it’s worth learning. I couldn’t get by without it.
Darktable is also extremely powerful, but if you’re shooting with a phone, it’s probably unnecessary, since it’s best used by photographers who shoot in RAW on DSLRs.
That said, I’ve never seen the need to remove clutter from an iNat photo, and I only rarely see the need to unfocus the background. I mostly use photo editing software for extremely basic operations (rotating and cropping) and for light sharpening and color correction.