I am really surprised that this is still missing. Garmin will write data to Apple Health, but will not read it. For diet tracking, I use cronometer. There is no way in hell I’m giving other apps access to all of whatever data Garmin has on me, so instead I have cronometer set up to read and write from Apple Health. Since Garmin writes there, it’s able to read select items that I control. This is how it should be done.
So instead, Garmin seems to have 1 integration option, with myfitnesspal (who got hacked and leaked millions of records, I might add). If garmin simply wrote data to Apple Health, they wouldn’t have to integrate with specific apps, they would all automatically work via Apple Health, and users would not have to consent to sharing agreements.
Why would Garmin not implement this? Apple makes it trivial, and you’d get support for not just MFP but all current and future diet sync apps that use Apple Health.