I have no good examples of this since I started this game at 3*, my LN + Note mastery comes from RoBeats doing LN Hybrid many, many times.
Get some mastery at tapping normal notes from every lane, though not necessarily at the same time unless youre feeling spicy. Then try to find if there's any sort of map which has you holding down on a lane while having to tap on the others. Also need LN maps which have multiple LN in a row, but every time an LN ends another starts and requires you to tap a normal note at the same time, meaning you're tapping 2 lanes at once while needing to hold one. They may combine both. That should build basic long note comfort.
Again, I don't know any good maps for example that aren't 4*+. I just assume it exists.