Me and my DM collaborate closely on his campaign, and I create most of the homebrews we use (I'm our artificer, so it works out pretty well for the both of us.)
Recently, I've found that DND beyond has stopped giving me the ability to edit other people's character sheets, meaning that my ability to add things to player inventories has been taken away. Is this the result of a setting we can't find, or an unfortunate update?

AFAIK, only the DM's ever been able to edit other people's character sheets.

(Though if you've been editing the homebrew items themselves, that still works.)

I misspoke. It's not editing the sheets itselves. Rather, it's being able to add items or use a sheet's roll stats. I couldn't go to the manage section, but I could still interact with the sheet.

Quote from Jackman003004 >>

I misspoke. It's not editing the sheets itselves. Rather, it's being able to add items or use a sheet's roll stats. I couldn't go to the manage section, but I could still interact with the sheet.

 
This has never been possible. The only people who can add items or click to roll dice into the log have only ever been the player who owns the character sheet and the DM of the campaign.