What exercises can you do to target the upper middle/inner part of the chest? Is it as simple as doing incline chest press?
AthleanX on YouTube has a (very old) video on working out the inner pecs which I haven't seen yet. This more recent video (and one that I have seen) talks about cable flies. This part of the pec is quite challenging and one of the best ways is to use a cable fly (one at a time) and try to cross the mid-line of your chest. In other words, you want to pull the cable slightly across your chest. That little bit of extra movement is what builds the inner pecs.
You can't target the inner chest, this is just where the muscle fibres attach to the sternum. The fibres contract along their entire length not in one select area. You can emphasise which fibres get activated though. As you said the incline bench will work as it emphasises the clavicular (upper) head of the pec major. Another useful exercise is the low to high cable fly. Aim to touch your elbows together at the top rather than your hands and the contraction will be much better.
The easiest exercise to achieve this is a standing cable fly and making sure you achieve maximum/peak contraction. However, just as Lux Claridge mentioned, it's also vital that you extend beyond your center line.
Because of this, I instead recommend that you practice a kind of incline compound dumbbell bench press, in where the first half of the press is the "standard" bench press, however, once your elbows reach a 120 degree angle, you then rotate the dumbbells inwardly 180 degrees so that by the time your arms are fully extended then the initial outer part of the dumbbells then touch inwardly.
This is truly the most effective exercise to maximizing activation of your inner upper pectoralis major muscle.
Edit: Once you reach full extension of your arms, it's good to hold that position for 1-2 seconds before resetting.