It looks like a platform and not something self-hostable, so you can just buy a domain and point these DNS entries to them which you can do in what's basically your domain's settings with your domain registrar: docs.bearblog.dev/custom-domai... No hosting or SSL setup needed

Custom domains

Adding custom domains to your Bear blog

I guess it's also worth noting you don't *need* to buy a domain upfront and can just use *yourchoice.bearblog.dev* and can always use your own later

oh sweet, that makes it much easier!