I tried running the /particle command with minecraft:wither_boss_invulnerable it shows the black particle for it. However, the log says something is wrong with the direction yet it works fine. Here is what it says:

[Molang][error]-Error: accessing a variable that doesn't exist: variable.direction.x

[Molang][error]-Error: accessing a variable that doesn't exist: variable.direction.y

[Molang][error]-Error: accessing a variable that doesn't exist: variable.direction.z

 I then tried other particles with the swirl thing in it, I used minecraft:splash_spell_emitter and minecraft:mobspell_emitter and I got this error for both of them:

[Molang][error]-Error: accessing a variable that doesn't exist: variable.color.r

[Molang][error]-Error: accessing a variable that doesn't exist: variable.color.g

[Molang][error]-Error: accessing a variable that doesn't exist: variable.color.b

[Molang][error]-Error: accessing a variable that doesn't exist: variable.color.a

Some swirl particles that don't give an error:
minecraft:evoker_spell

Other particles:

minecraft:basic_crit_particle

Log:

23:22:51[Molang][error]-Error: accessing a variable that doesn't currently exist in this entity: variable.direction

23:22:51[Molang][error]-Error: unable to find member variable .x

23:22:51[Molang][error]-Error: unhandled request for unknown variable `.x`

23:22:51[Molang][error]-Error: accessing a variable that doesn't currently exist in this entity: variable.direction

23:22:51[Molang][error]-Error: unable to find member variable .y

23:22:51[Molang][error]-Error: unhandled request for unknown variable `.y`

23:22:51[Molang][error]-Error: accessing a variable that doesn't currently exist in this entity: variable.direction

23:22:51[Molang][error]-Error: unable to find member variable .z

23:22:51[Molang][error]-Error: unhandled request for unknown variable `.z`