as mentioned above, it isn't
for a brief summary of ungiftables (some possibly missing, someone correct me if I made an error anywhere)
all trophies+ribbon
rainbow feather
all animated collectibles
fair patches
raffle entries
special snowflake
holiday candy canes
golden christmas candy
pink candy
dark candy (also nearly unobtainable)
dusty scroll
ancient lantern
fire festival collectibles
golden egg
easter bunny
game icon collectibles
astral inner planet floating gold #10
corrections
nearly all account upgrade features, with the exception of the small mailbox
turnips
fertilizer
bell bag
and with the possible exception of the gold candy being changed to be giftable if rereleased, like how the christmas candy was last year, everything in this list should be treated as permanently ungiftable until further notice
also, while not ungiftable, you can only gift birthstones (and I assume valentine's roses) once before they're locked to a single user