Sir Francis Drake: pirate.
But he was referred to as a “privateer” by the crown.
He was a pirate.
No matter how you dress it up, it’s still a mercenary.
Everyone fighting for Ukraine is legally in the Ukrainian military and is required to be treated by international POW law.
Since you won’t answer I have to assume that you think the French Foreign Legion goes to war legally defined as mercenaries rather than French soldiers and if captured are under mercenary law rather than regular POW law.
Why don’t you post a reputable source that defines soldiers officially serving in a country’s armed forces as being legally a mercenary and under mercenary law?