Not exactly true, if there is indeed a yuri moment occurring a futa being present will not nullify the need for the tag. As long as one girl is doing a yuri act to another girl, it should count as yuri. Ruby having a penis doesn't nullify Penny fucking Weiss with a strap-on, since both are taking place it's both yuri and futa_with female.
GoldSaw said: Ruby having a penis doesn't nullify Penny fucking Weiss with a strap-on, since both are taking place it's both yuri and futa_with female.
Yes it does. It's exactly the same as if the penis was on a guy instead.
I tried searching for bisexual (female)strap-on. None of the results are tagged as yuri, except for a few pictures showing orgies that actually feature isolated girls-only acts.
If a strap-on doesn't make a bisexual act yuri, neither should it make a futa-on-female act yuri.