Intervals.icu can now process the file Garmin sends you when you request all of your data. This isn’t a quick process (Garmin take days to respond) but you get all of your activities with their Garmin Connect names and wellness data.
Currently wellness import is limited because I haven’t seen what the data for weight etc. looks like in the files. If you have other wellness data and want it to be imported into Intervals.icu mail me (firstname.lastname@example.org) the link Garmin sends before doing the import and I will have a look. Tx.