Does Explorer have Track Back?

I do not believe that the Explorer has track back. I no longer have an active legacy device, so I cannot check.

Again, refer to the manual for instructions on navigation. The short version is that you can navigate to a waypoint or you can follow a pre-designed route. Since the Explorer has no maps (the Explorer+ does), it is difficult to mark a waypoint at a remote location in the field. You can easily mark a waypoint at your current location in case you later need to return to that spot.

https://static.garmin.com/pumac/inReach-Explorer-Manual.pdf

Remember that the Explorer/SE and Explorer+/SE+ are legacy devices. They were designed by DeLorme before Garmin purchased the company. The are not (and never will be, IMO) full members of the Garmin ecosystem. The inReach Mini has a foot in each ecosystem, but has no maps and is somewhat difficult to use.

Options like GoTo and Find require a POI database on the device. If you are interested in features like that, you will have to abandon the legacy Explorer/Explorer+ and invest in a newer inReach device. For example, the GPSMAP 66i and the Montana 7x0i are full members of the Garmin ecosystem. They support the full range of Garmin maps, as well as Birdseye imagery.

I use my Explorer a lot from October to January 31st. I've got an Instinct watch with "TrackBack" but as best I can tell, you have to begin navigation before you leave, in order to have something to TrackBack to.

The Explorer doesn't call it "trackback" but the same feature (as best as I can tell) is "Tracking" and if you start tracking before you leave you'll have a visible route you can track back. Remember to start tracking, or you got nothing. If there's a clever way to set it up so that it always tracks upon startup, I haven't figured out how. EDIT: Yes you can, under "Settings" - "tracking" - Auto-Track - on or off.

It does not have the GoTo like other units. With Explorer, this feature is essentially the same as choosing "Waypoints", select a waypoint, (they are sorted closest to farthest), then select  "Navigate", and you're on your way.

Yes, true track back requires you to be tracking before you engage track back. On units which have the feature, engaging track back navigates your track backwards, from where you are now to the beginning of the track. This is active navigation, and will give you (at minimum) a "pointer" telling you which way to go to the next track point in the backward direction.

The Explorer does not have this feature. As you point out, you can visually navigate back along your track. But the unit will not give you navigation aids such as the "pointer".

You are correct about navigating to waypoints. However, this only takes into account waypoints on the unit. Unlike some newer devices (for example, the 66i), the unit does not have  POI database - so there is Find function.

The only thing I can find on my Explorer+ is if you go to History (page 2), then you can see the points you just came from and click navigate.  However, they aren't labeled by time so you'd have to click on each one separately.  Not ideal in emergency/darkness, but is something.