At-will employment and "right-to-work" are distinct ideas. The first has some real benefits, while the other is just union-busting bullshit.

At-Will Employment means that the relationship of employee to employer is technically voluntary. Your employer can fire you or lay you off for almost any reason or no reason, but you are likewise free to just walk away without even finishing your shift and get another job. (Non-discrimination laws and professional continuity-of-care rules are common exceptions.)

Right to work doesn't affect whether or not your employement relationship is voluntary. Instead, it means only and exclusively that you can freeload off the union, getting all of their benefits and leaving them with all of the expenses of negotiating your salary and work rules.

In the USA most (but not all) states are "at-will employment", and most red states have the same sort of bullshit anti-worker "right to work" laws that MLK was campaigning against when he was murdered. And, unfortunately, thanks to SCOTUS fuckery all of the USA is essentially "right to work" since the same assholes behind "corporations are people" and "money is speech" decided that payroll deductions for union dues are terrible in way that payroll deductions for taxes or insurance aren't.