This applies to iOS v15 and v16. For older versions, see the v14 guide.
Download the certificate to your Downloads folder
Open your Downloads folder and click on the certificate
Head to Settings > General > VPN & Device Management
Locate the profile and tap on it
Tap Install again
Tap Install yet again
You should see green text with a check-mark saying “Verified” under the Profile Installed dialog.
Next, navigate to General > About > Certificate Trust Settings.
Under “Enable full trust for root certificates”, enable “Embassy Local Root CA”.
Your certificate should now be installed and trusted: