I just setup a local https dev domain wildcard (*.internal) with mkcert and caddy a few days ago - working great on all my devices and only took a few hours to figure out and get working.
FYI if you're using Caddy, you don't need mkcert. Caddy has smallstep built-in which does the same thing, automatically.
If you're not using .local or .localhost, just add `tls internal` to your config to make Caddy issue certs using its local CA. Caddy attempts to auto-install its root CA cert, just like mkcert (almost identical code, in fact; see https://github.com/smallstep/truststore).
