There is no transfer agreement between the KHL and the NHL due to Russia's aggression towards Ukraine. Bettman has nothing to do with this at all.
When there was an agreement the player could buy out his own contract but could not use funds from the team that he was transferring to. Rotenberg's heavy handed behaviour is very common in Russian bureaucracies and this was to be expected.
I guarantee that this is as much or more about Rotenberg's ego vs western media and western social media narratives than it is about Demidov himself.
The NHL and KHL never had a proper transfer agreement. It was merely a MOU agreeing to not poach players.
The NHL later suspended their end of it but Bettman told the KHL they’d still abide by the spirit of the agreement.
The NHL’s prohibition on reimbursing, or fronting money to KHL clubs is an internal NHL matter - and still in effect AFAIK.
It’s why the Flyers had to go ‘under the table’ to front Michkov money so he could afford his buy-out fee.