This is the Ray of Sickness Spell, I tried adding it to a homebrew feat. It doesn't exist.

Same thing with Infestation.

Do you own the PHB and Xanathar's on DND Beyond? It looks to me like they're being shared with you -- shared content can be read and used in the character builder, but you can only use content you own when making homebrew.

That makes sense. I didn't even realize it was being shared.

Thank you

Here is a list of all the spells you can attach without purchasing any. It’s all the stuff that WotC publishes for free.

https://www.dndbeyond.com/spells?filter-class=0&filter-search=&filter-verbal=&filter-somatic=&filter-material=&filter-concentration=&filter-ritual=&filter-sub-class=&filter-source=1&filter-source=4&filter-partnered-content=f