This will work on stock Android, and equally well on CalyxOS, GrapheneOS or LineageOS.
Warning
This is only possible on Android version 12 or greater. For LineageOS, that corresponds to v19+.
Tap Settings > Security > More security settings > Encryption & credentials > Install a certificate > CA Certificate > Install Anyway and select your “Embassy Local Root CA” certificate.
Tap Settings > Security > Advanced > Encryption and Credentials > Install from Storage and select your “Embassy Local Root CA” certificate.