What does "after work" mean when you are expected to respond to email & Slack/Teams after you leave the office? The tradeoff to being always available to work is there's no "after work" time anymore; jobs have already claimed all the waking hours.
It's a matter of setting boundaries. If you do work whilst not getting paid, the beneficiary is not going to correct your error. The only way you get them to pay for 24 hour availability is by not working 24 hours each day for free.