I don't know who needs to hear this, but maintenance of strength and muscle can be achieved with surprisingly little volume, even just 1 day per week. Multi-joint exercises like pull ups, squats, presses, and rows should be prioritized over isolation exercises.
But if you decide to add an isolation exercise, the dumbbell curl is a great place to start.
Going to the gym is more than just a workout. It's proof to yourself that you're willing to fight to become the person you want to be. Don't let that version of yourself down.