I believe this is because its on the bard's optional spell list from tasha's rather than the main spell list.  However when adding spells for the ritual caster (bard) Telepathic Bond/ Rary's Telepathic Bond doesn't appear.

That is because the spell if a 5th level spell and is unable to be added via the ritual caster feat, which has a built-in spell level limitation. When you get the feat it adds 2 level one spells and if you add a spell after that its level can not exceed half of your level rounded up. 

If you are able to add other 5th level spells, but just not specifically that one, it may be a different issue, and please let us know.

There are no other 5th level ritual spells for the bard.  However the character is 13th level.  If I switch the feat to ritual caster (wizard) I have the spell as an option.

Yeah, it's because it's not technically on the Bard spell list.

What you can do is create a homebrew copy of Telepathic Bond, call it like "Telepathic Bond (TCoE)", and in Basic Information have it just be on the Bard spell list.

I had to do similar things with Wizard spells for my Arcane Trickster with Ritual Caster (Wizard).

Quote from naruhoodie >>

Yeah, it's because it's not technically on the Bard spell list.

What you can do is create a homebrew copy of Telepathic Bond, call it like "Telepathic Bond (TCoE)", and in Basic Information have it just be on the Bard spell list.

I had to do similar things with Wizard spells for my Arcane Trickster with Ritual Caster (Wizard).

 Thanks that worked. I suspected the reason.  I just didn't know the feat was smart enough to pick up homebrew considering it didn't pick up the fact that I had enabled the optional spells.

Technically, you only get access to the optional spells for a spellcasting class from being that spellcasting class. It's the way Tasha's was written; since it doesn't specifically add those spells to class spell lists, by rules as written we don't get to access them, and DDB has to implement rules as written, unless WotC publishes an errata for the book that's more definitive.

But of course many DMs like mine think of course they should be on the spell lists for the purpose of Feats and third-caster classes, and that's where the homebrew tools help us get access to the spells, roundabout as it is.

I'm taking Bard ritual caster as a bard so this wouldn't disqualify me either.

Quote from naruhoodie >>

Technically, you only get access to the optional spells for a spellcasting class from being that spellcasting class. It's the way Tasha's was written; since it doesn't specifically add those spells to class spell lists, by rules as written we don't get to access them, and DDB has to implement rules as written, unless WotC publishes an errata for the book that's more definitive.

But of course many DMs like mine think of course they should be on the spell lists for the purpose of Feats and third-caster classes, and that's where the homebrew tools help us get access to the spells, roundabout as it is.

Unfortunately the system is not that smart. All it knows is that the TCoE rules are considered optional rules for bards, and that the person taking this feat might not be a bard. Do all bards automatically get this spell? No. Then it's not programmed on the list of spells available via this feat.