Cantrip Expansion is a common Class Feat among casters.

Is Cantrip Expansion worth it? Is Cantrip Expansion good?

For prepared casters (Cleric, Wizard, etc.), definitely not.

For Spontaneous Casters (Bard, Sorcerer, etc.), probably not. I'd rather have my generally useful cantrips on my character and then create specialized staves.

https://2e.aonprd.com/Feats.aspx?ID=183

People seem to love teh feat but you shouldn't be using it -- make a personal staff (or two) instead.

Creating a Personal Staff https://2e.aonprd.com/Rules.aspx?ID=1500

Staves https://2e.aonprd.com/Rules.aspx?ID=748

It may also be counter-intuitive but it probably makes more sense to have your most commonly used cantrips in the staff (and not prepared). The thought process? It's easier for prepared casters to swap out their cantrips during daily preparation than it is to create (or find) a new staff.

Staff of Fire https://2e.aonprd.com/Equipment.aspx?ID=356