The 6th level ability Spirit Session allows only divination and necromancy spells but the drop down shows all spells.
Bard College feature PHB p51[–] At 6th level, you gain a feature from your Bard College. Spirit Session VRGR p28[–] 6th-level College of Spirits feature Spirits provide you with supernatural insights. You can conduct an hour-long ritual channeling spirits (which can be done during a short or long rest) using your Spiritual Focus. You can conduct the ritual with a number of willing creatures equal to your proficiency bonus (including yourself). At the end of the ritual, you temporarily learn one spell of your choice from any class. The spell you choose must be of a level equal to the number of creatures that conducted the ritual or less, the spell must be of a level you can cast, and it must be in the school of divination or necromancy. The chosen spell counts as a bard spell for you but doesn't count against the number of bard spells you know. Once you perform the ritual, you can't do so again until you start a long rest, and you know the chosen spell until you start a long rest.
The 6th level ability Spirit Session allows only divination and necromancy spells but the drop down shows all spells.
Bard College feature PHB p51[–] At 6th level, you gain a feature from your Bard College. Spirit Session VRGR p28[–] 6th-level College of Spirits feature Spirits provide you with supernatural insights. You can conduct an hour-long ritual channeling spirits (which can be done during a short or long rest) using your Spiritual Focus. You can conduct the ritual with a number of willing creatures equal to your proficiency bonus (including yourself). At the end of the ritual, you temporarily learn one spell of your choice from any class. The spell you choose must be of a level equal to the number of creatures that conducted the ritual or less, the spell must be of a level you can cast, and it must be in the school of divination or necromancy. The chosen spell counts as a bard spell for you but doesn't count against the number of bard spells you know. Once you perform the ritual, you can't do so again until you start a long rest, and you know the chosen spell until you start a long rest.
This is a known issue and a flaw with the system. For the moment, just make sure that you pick a spell from within the required specifications.
Buyers Guide for D&D Beyond - Hardcover Books, D&D Beyond and You - How/What is Toggled Content?
Everything you need to know about Homebrew - Homebrew FAQ - Digital Book on D&D Beyond Vs Physical Books
Can't find the content you are supposed to have access to? Read this FAQ.
"Play the game however you want to play the game. After all, your fun doesn't threaten my fun."