GPS spoofing and accurate distance measurement

In the sensor menu under HRM Pro you can select when the strap's step based estimates are used instead of gps. If you've run enough with the strap and reliable gps, the auto calibration has probably already happened. If you select "always" for distance, the watch prefers strap-based distance estimate over gps also in outdoor activities. A similar option exists for pace.

It might also be worth trying different GNSS settings, like would Glonass give better data? I would think this depends somewhat who is doing the jamming, what GNSS they will be jamming. 

Or is everyone nowadays using all the GNSS that one needs to jam all of them..... but then the jammer is kind of also shooting itself in the leg.

At least on 965 the only options are GPS or "All systems" (+ SatIQ/Multiband etc.). There isn't any more options to select other individual GNSS systems like in older watches.

Ah, true.. That's kind of bummer. Haven't had the need, so kind of assumed, one could still do that...  but now that I think, I think in the older ones it was also like GPS + GLONASS or GPS + GALILEO. Not like without GPS... 

I would appreciate it if Garmin could automatically detect during a workout when something is amiss, such as discrepancies between heart rate and distance or steps and distance, and then the watch will take the following actions:

1. use GPS (if workout is not indoors workout)

2. if distance or/and pace does not correlate to steps count, prefer distance / pace based on steps

on 955 the options are:
1. Off

2. GPS only

3. all systems

4. all + multi band

5. Auto select

6. ultraTrac

I think the new Fenix has something like this:

"Now interestingly, one feature that’s somewhat hidden away, is a new option to automatically process GPS tracks for correction, using internal sensor data. Meaning, if the watch detects that the GPS accuracy was non-ideal during the workout, it’ll flag the file to be analyzed by Garmin Connect online, leveraging the sensor data inside the watch (e.g. accelerometers, compass, gyro, etc..) to try and correct for said bad GPS data. This is specifically for only pedestrian activity and openwater swims (since those are activities that can look at things like arm movement to try and normalize against). The concept sounds roughly akin to what Suunto has previously called ‘FusedGPS’, except it sounds like Garmin is leveraging cloud compute to likely run more variables. Note that map data isn’t part of the correction set (whereas Apple, for example, does use map data for the corrections)." ref. Garmin Fenix 8 In-Depth Review: Worth the Upgrade? | DC Rainmaker 

Apparently they call it "Position Enhancement", didn't still find it from the manual, but apparently the setting is default on. Otherwise finding very minimal information about it..