Managing my supervisor’s expectations when we are understaffed?

I’ve worked this job for 1.5 years. The team I work on is understaffed (and has been for the past 6 months) and my manager can’t hire a replacement quickly due to a hiring freeze. When my coworker left, I was saddled with their responsibilities which has been hugely stressful. I feel that my supervisor hasn’t moderated their expectations at all in light of our staffing issues and seems to expect me to maintain the priorities of two people. I’ve tried expressing this, tried being clear about my priorities and what will be deprioritized as a result - but it’s usually met with “well those other things need to be prioritized too”. What really has sent me spiralling is that last week during a performance review, my two managers said they’ve been noticing I haven’t been meeting deadlines as well lately and certain things have been falling off. I reiterated how much I’ve had to take on since my coworker left and that I’m open to their prioritization of things as it seems theres misalignment. Admittedly things have been dropping off and I didn’t meet some soft deadlines in December due to the amount on my plate. My managers were pretty dismissive and now during my weekly check in I’m being saddled with even more responsibilities and told that it’s a normal workload. Every issue I flag during the course of work seems to just annoy my supervisor. I feel like such a nuisance to my supervisor and it really sucks because this is my first permanent role and I wanted to stay longer (I transferred from a contract-based industry). It might be the anxiety talking but I kind of feel like they want to fire me but can’t due to staffing (also my position is union and they haven’t issued any formal warnings). Do you have any advice that I could try or do you think it’s just time to move on?