The transition from home to formal residential care is described as stressful and emotionally difficult for people with dementia and their informal caregivers. While HCI research investigated how technology supports people with dementia at home or in formal care, there still is a need to understand how technology can support care transitions. This paper presents a practice-informed approach to gather insights collaboratively between care professionals and HCI researchers. We interviewed 42 informal caregivers of people with dementia to uncover their experiences before, during, and after care transitions. Our findings reveal how informal caregivers were: 1) navigating hurdles of information on care transitions, 2) caught up in the evolving challenges of informal caregiving, and 3) shifting from uncertainty in decision-making to acceptance of admission. Next, we formulate six design opportunities to support transitions in dementia care and encourage HCI researchers to pursue a practice-informed approach to address societal challenges in dementia.