Its easy to think that because some gameplay you have doesnt feel fun, that its because of the high level mechanics (that you would normally think as the gameplay). But I feel that usually, 90% of the experience is determines by the 'not gameplay' things. Graphics, music, visual and sound effects, side effects of the primary action, and what purpose the gameplay serves (challenges are usually part of a bigger challenge that gives meaning to the subchallenge).
Consider that even if your gameplay doesnt even exist (the player just passively sits there), it can still be amazing. Thats how movies/music/books work, after all.
So, at the minimum, gameplay just needs to not get in the way, and that can be enough if supported by other content/effects. Maybe you do some basic actions that require zero thought and achieve progress, and repeat.
Of course, if you can tie in some exciting and cognitively interesting tasks, thats great. Make the player choose or build optimal/preferred solutions. Make it rely on their understanding of the games systems. Add some time pressure / risk. Make the consequences of however they act, meaningful.
Just understand that not all gameplay needs to be like that. It can even be exhausting for the player if you require constant focus on solving difficult problems.