I've made a custom magic item that lets a PC cast a series of spells once per day each. When adding spells to the item in dnd beyond, the only option I have to stop it granting the PC the spells at will is to make it cost charges, which is not what I want to do at all.

Is there some sort of setting that I'm missing?

No, you’re not missing anything.

So there's no way to limit spells to once per day?

Quote from ElishaBrightshield >>

So there's no way to limit spells to once per day?

 

 Currently, no. It's even an issue with official magic items like the various Instrument of the Bards.

I implemented a workaround for our party Bard by putting the spells into a homebrewing a Feat, and homebrewing a base "Instrument" that doesn't contain spells or charges. Unfortunately we can't implement a Feat prerequisite for "must be attuned to {certain magic item}", but it worked.

The someday-coming overhaul of the system should take care of this issue, given that it affects official items much less homebrew.

I'm making a staff that has this benefit:

• You can choose to know 7 additional spells of your choice from the sorcerer, warlock, or wizard spell lists. The spells must be of a level for which you have spell slots.

What modifiers do give it to have the choice of spells.

Quote from Demonslayer36525524 >>

I'm making a staff that has this benefit:

• You can choose to know 7 additional spells of your choice from the sorcerer, warlock, or wizard spell lists. The spells must be of a level for which you have spell slots.

What modifiers do give it to have the choice of spells.

 
None. You cannot include a choice of spells on an items you will need to learn what spells the player wants and create the item with those specific spells attached.