Quote from EquesInvictus >>

So the drop down under feats does not include ritual caster (cleric) as a choice for my Paladin. For my rogue I found it easily. I am wondering if this is a malfunction because the Paladin is a partial caster

Go to your character sheet - Features - and then Feats. Does the character already have the feat? Because that would stop it showing up.

If it does - then click Manage Feats on the same page and remove it if possible - if it's not possible you must have it from an ASI or race in the builder.

And if that's not it - it would really help if you linked the character so a mod could take a look to see what the problem is.

Here is the character: https://www.dndbeyond.com/profile/EquesInvictus/characters/47338957

I found the feat with my ranger and rogue.

Ritual Caster requires an Intelligence or Wisdom score of 13 or higher. Your Paladin has neither. That is probably why.

Ritual Caster (https://www.dndbeyond.com/feats/ritual-caster)
Prerequisite: Intelligence or Wisdom of 13 or higher.

That was exactly it thank you

For Pact Tome Warlocks, how do we add ritual spells? It doesn't seem to have an option for that when you manage your class abilities selection.

Quote from Felwred >>

For Pact Tome Warlocks, how do we add ritual spells? It doesn't seem to have an option for that when you manage your class abilities selection.

It's not the Pact of the Tome feature itself that lets you do that. All Pact of the Tome does is give you 3 cantrips. The feature that lets you add Ritual spells is the Book of Ancient Secrets Invocation.

The Ritual Caster Feat doesn't display all the spells in the book even if you have learned multiple spells already. Is this a bug?

https://imgur.com/a/ogTCbUS (What is displayed)

https://imgur.com/a/7FhJubc (Spells I actually have)

It worked fine for me on a test character. It might be the cache problem (which usually presents with something being selected multiple times by accident, not not appearing, so I'm not confident). Try removing them and adding them again. Either way, provide a link to the character (use the URL, not the 'share' link) so mods can take a look.

Also having issues with Ritual Caster not allowing more than three choices to be added to spell lists. 

ddb.ac/characters/14484476/KI39qS

Quote from Glixile >>

Also having issues with Ritual Caster not allowing more than three choices to be added to spell lists. 

ddb.ac/characters/14484476/KI39qS

 It looks like you have a bunch of spells added via Ritual Caster (Bard). If they aren't all showing up, try reloading the page. Or... what exactly do you mean by "not allowing more than 3 choices"?

Also for some reason you have Comprehend Languages added twice from the feat. I have no idea how you managed that.

(Edit: Okay I just checked on my own character's Ritual Caster feat, and it is possible to accidentally add the same 1st-level spell 3 times: for each of the 2 freebies, and once from the "anything else copied in" dropdown. I suggest removing one of those duplicates, which you can do by changing its dropdown back to "- Choose a Spell -".)