In theory you could use MRA Web on Chrome on the iPhone and the Garmin Drive App on your iPhone to do the transfer using the GPX1.1 (BETA Route, Track, POI)
Plan on the MacBook, switch to the iPhone to do the transfer.
Use the Chrome Browser as Safari will not give you the “Open In” option for the GPX file and will force you to “Save to Files”.

If you need to create a collection on the XT you have to do it using the Explore Website not the Explore App and you must also have the Garmin Drive App open as well.
Then on the XT if you “Sync” using Explore the collection you created on explore.garmin.com will pull into the XT.
Why we can’t just create a Collection directly on the XT is ridiculous. 🤨