Aura

I like the Zelda approach of making secret walls very visually distinct. Honestly it's the only approach I like, I hate how Pokemon conditioned me into clicking absolutely all trashcans / rocks in every game I play

i think the best way is to clue literally every secret and make them more impactful/puzzly to find. if you find a secret it's because you figured out that something had to be in the place that you found it through some external clues rather than just stumbling into them by accident

if secrets are puzzles and puzzles are distinct "ah ha" moments then secrets are "ah ha" moments

but that's a lot more design work and not the kind of thing most gamers think of when you say "secret"

Another thought would keep one or more classes of secrets off of any progress tracker? Though I don't know if that'd help or just frustrate

My thinking is that sometimes the tedium can come from completionism.

That being said, there are more than a few folks that try to find all of the koroks in BoTW/ToTK, soooooo

You could put a note on the title screen of your game that there are no breakable walls and you best believe I'm still smacking every single brick with the fury of a man whose parents were killed by stonemasons.

I'm kind of the opinion that breakable walls are fine... I think a lot of the fun in secret hunting is getting an intuitive understanding of the nebulous rules around how and where they are hidden in a particular game. Dark souls is an example of this, some walls just look suspicious, they're weirdly flat, maybe you can see some area that looks walkable behind it, and I find that kind of problem solving really satisfying.

Explicit cryptic puzzles are also always a good time, I specially like when you have to connect info from different areas of a game (mostly applicable for exploration based games)