tag @s remove veer.ecf.isGlowing
# Is glowing?
tag @s[nbt={Glowing:1b}] add veer.ecf.isGlowing
# Toggle
#   1 -> 0
data modify entity @s[tag=veer.ecf.isGlowing] Glowing set value 0b
#   0 -> 1
data modify entity @s[tag=!veer.ecf.isGlowing] Glowing set value 1b