I want to hire a dedicated mobile app developer who can work for me as a full-time freelancer. If you have any good suggestions please let me know.
I'd check out UpWork. Just be very clear about your requirements and make them use a time tracker if possible. Ensure that they are communicating effectively and that you have full visibility on the work and where they are spending their time/effort.
Also, you might want to get someone who audits their code or does QA. That was my mistake when I tried launching my own photo app in 2016. The thing ended up being riddled with bugs!