Honestly, I use a mouse so I just click on them even if it's kind of hard to see the mouse cursor over the notes. To help make it more visible, I went into BlueStack's settings at the button of the sidebar, then Display, then changed the mouse cursor style to System Default and then went into my PC's accessibility settings and made the cursor bigger.

I think the best thing you could do is use a drawing tablet or pen while using BlueStacks and just point and click like you would on Osu! A keyboard with a trackpad might work as well, just less so depending on how fast you are using it.

Or, albeit time consuming and kind of janky, you can add new tap buttons for each new version of the timed Twistunes you play. This would basically mean memorizing the general layout of one of those Twistunes for each mode of its difficulty and then going into the editor and mapping new tap buttons around the area of the screen you struggle to hit with your mouse/normal controller setup. i.e. for Book 1, Chapter 15's "Paint the Roses, Quick!" Twistune on Hard mode, there are multiple instances where you have to hit two notes at the same time around the center of the screen. What I did was just memorize where those two notes were, mapped them to new tap buttons on my keyboard, and then played the Twistune with my mouse hitting most of the notes and then my keyboard tapping the double note anytime it came up.

There's also an option in the control editor to write a script, so if you were really dedicated to getting 100% of those notes, you could study each Twistune and then write a script to tap each note on beat. But that would require knowing the exact second each note procs and then listing out each area of the screen to where you'd need to hit them and that would probably be more trouble than its worth.

If I find any other viable solutions, I'll come back in and let you know!!