@Lighted_Candle, thank you! The problem is: in the New Products sheet, each book has a Category column where up to 5 categories per book can show up, separated by commas. There’s then 5 columns - Category 1-5 - with a formula to split those categories.
So, each category relation column in the Users Preferences sheet would have to relate to each of the 5 Category column in New Products. I can’t understand how to do this…
I had opened a new post for this: How to filter by signed-in user - Glide doesn't show automatically created Users relation column
My app: https://t3wff.glideapp.io
Google sheet: https://docs.google.com/spreadsheets/d/1NDPEhQztlho_V22qSpUgm4U29Oay6A9mDewBfR3H3ec/edit?usp=sharing
Thanks!