You know, at a minimum, playing by ear requires you to hit ONE right note and hold it there with your acquired rhythm skills. And the chance of hitting a right note in a western scale or mode is at 8/12 = 66%.
So my first tip would be to let a tune run in the background, something you like, then find a note on the piano that works with what you are playing. Then try again with another note. And again, and so on. Enjoy this process, treat it like play as much as you treat it like practice.
Second: learn a few scale patterns (if you haven’t already). Basically you’ll need the major scale pattern (W W h W W W h) and the minor pattern (W h W W h W W).
Once you’ve got those down return to the first exercise and once you found a note, try to find the corresponding scale (using the major / minor patterns from the note you’ve found).
This becomes easier as you get better at finding the tonic / key / root note to a tune…here’s a tip on how to do this…listen to the tune and eventually try to hum along, just one steady note. Keep going until you find a note that sounds right…hold it and see if it works with different parts of the song equally well…if so you’re likely to have found the root. Focus not just on sound here, try to FEEL the resonance that your note creates in your chest / body as it mingles with the music, it’s ACTUALLY a physical sensation. If that vibration is maintained across the tune, you’ve got the root.
Now try to find that note on the piano, still humming it of course. once you have that note, use your knowledge of major/minor scales to find the right scale (whatever sounds better) — now you’re good to improvise, first melodically and if you dig that you can progress to play with chords on that scale.
The more you do this, the more it will become a feeling and second nature. And yes, you (and everyone else) is capable of this with 100% certainty.
Use your ears AND your body to guide you!