I agree that there are no magic solutions, no particular drills to play which will suddenly transform your technique. Anything that focuses purely on mechanical process rather than on the relationship between process and resulting tone production may well assist in finger agility, but will not turn you into a better pianist. At your level, the path to a great technique is best explored through detailed attention to perfecting repertoire.
Developing piano technique is a journey - a journey of discovery.
What's important:
1. RELAXATION
Become very aware of your body as you play. Avoid tension as much as possible. Allow larger muscle groups in your arms and hands to control your playing, rather than thinking of playing with your fingers all of the time.
2. Regarding fingers, focus on JOINT STABILITY, rather than curled/curved/flat.
I have a video on the topic of joint stability on my YouTube channel.
The video is aimed at an audience who is certainly not playing at your level, but, depending on your approach to playing the piano, you may find it nonetheless helpful.
3. Make up EXERCISES based on your repertoire.
Extend short patterns that you find in your pieces.
Practice in tiny fragments 1 beat, 2 beats, 4 beats, etc.
4. Have a clear idea of how you want each tiny part of a piece to SOUND. Decide at all times which muscles to use to achieve the desired sound. How much weight do you need to use? Should it be arm weight? Should it be the controlled weight of the hand? How much should the wrist be involved? Does angling the wrist facilitate the motion and result in a smoother sound?
Piano technique, to me, is nothing, if not a means to an artistic end. The pursuit of it through endless repetition of Hanon, Dohnyani, etc, can actually do more harm than good.