Strictly speaking they were always illegal in Russia anyway, which is one of the reasons why they only opened an office in Russia last NovemberWell we shouldn't be seeing any more Wagner patches now
https://www.bbc.com/news/uk-66724396
From about a quarter of the way down
The proscription order will make it a criminal offence to support the group - including by arranging a meetings aimed at furthering the organisation's activities, expressing support for its aims or displaying its flag or logo.
But laws don’t count in Russia if your Putins mate and / or pay him off.
…. and of course Wagner never were mercenaries, they have always been a deniable part of the Russian army