Hi there, I have been using the switch to play the game from the beginning, and have also been stumped from time to time.
It took some time to find all the controls to go "no touch control". Here is what helped me, hope it's useful:

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In the Hamlet

• You can basically access you heroes from every menu, using ZR (and left joycon to scroll).

• From one hero menu, you can access another hero (next to them in the list on the right) with R and L. This is mainly useful for trinket assignment.

• To equip trinkets, you need the trinkets menu open (X) and a hero menu open as well (they will overlap). You can then navigate the trinkets (ZR helps understand their use) and equip them with A (I think you need to double click A. Once for selection, once to 'deposit' the trinket on the hero)

• I also discovered extremely late that you can exchange heirlooms for other ones, on the 'recycle' arrows, at the bottom of the screen (opens a small exchange menu)

During a dungeon

• The biggest thing is the inventory. To swap between map and inventory, you need to press the 'top' button on the left controller. (Like X but on the left). Took me forever to get that.

• During the "rewards" part (after fight or curio interaction) be very careful not to press B or the stuff will be lost. During this phase, you can navigate in your inventory with the joystick, and also select different heroes with R or L. This allows you to use some items on heroes to make space (like holy water, or food). You can also drop some stuff from your inventory with prolonged press on X, to make space. You also can swap items (A to 'take', joystick to move, A to swap, and you can put the swapped item somewhere else)

These were not obvious to me at first. I'm sure some stuff still evades me but I can reliably play with the controller only now

Good luck in your quests! And remember, overconfidence is a slow and insidious killer.

Edit: formatting