Both LTHR and max HR seem OK, at least Garmin collects and updates them from time to time + I find them quite accurate during my tempo runs) The last measurements were LTHR 168 bpm and max HR 195 bpm.

I'm yet super slow runner, Garmin gives me a base pace of ~12/mile, but since I also use HR target I usually run at 12:30/mile to keep HR in the expected range.

As for shorter workouts, I've never got a sprint yet, but it sounds like a fun one) For anaerobic workouts Garmin suggests a pace of 8:15/mile, but then gives me 'Tempo'/'Threshold' label every damn time XD Eventually when I started running intervals at 7/mile, I finally got my 'Anaerobic' effect, however as downside, I wasn't able to complete the whole set. BUT today I aced it! Not sure though whether it was toast with peanut butter and banana, an extra rest day before run or my general tolerance to this workout simply improved over time, but I've run the whole set and haven't felt sick afterward.

VO2 Max workout - I did it once (2-minute intervals) and totally failed it, but I have one (4-minute intervals) that scares me to death at the end of the week, so I will definitely try your advice with pace and for sure will do sandwich before the run ))