Yup, you are not using a belt.

When I built up my Rohloff touring bike, I decided before I even ordered the frame that I would want two sets of gears, a lower range of gears for heavy touring and higher range of gears for mostly unladen riding around near home. When I go on a tour or come home from a tour I swap chainrings and add or subtract a few chain links. But, I do not mind spending time working on a bike. Most people want to have one range of gears for all things where I prefer two. You should decide what gearing you want early on and will that be for all riding or not.

It is my understanding this is a used Rohloff.
1 - When was the last time the oil was changed? 2 - When you build this up, chainline is something you should try to get close to right. Mine has about 5mm of chainline error, this was intentional on my part as I did not want my Q factor too big. https://www.rohloff.de/en/service/ha...embly/crankset
3 - I think most people do not mark their sprockets or chainrings (even number of teeth only) with which teeth should have the chain links with outer plates but I do. The teeth with inner plates get more wear as the chain elongates. https://www.sheldonbrown.com/chain-life.html
4 - Is the rear sprocket worn out? You can flip them over, then put wear on the other side of the teeth, does it look like that was done yet? An older hub will have a threaded sprocket, newer is splined and held on with a spring circlip. The older needed a special Rohloff tool that I assume you do not have to remove it.

Some people complain that their threaded sprockets are hard to remove, but I find that it is easy to remove if you have large tools. The newer spring circlip version is easy to pry off the spring, no big tools needed.