title does not take into account rawtext. It will only use the text itself.

/title @p title {"rawtext":[

{"text":"Hello World"}

]}

/title @p subtitle {"rawtext":[

{"text":"Hello World"}

]}

/title @p actionbar {"rawtext":[

{"text":"Hello World"}

]}

 

However the same format works in tellraw

/tellraw @p {"rawtext":[

{"text":"Hello World"}

]}