Today's run was much more encouraging. First of all, it was the farthest I've run continuously outdoors without taking a walk break, at a full 5 miles. I also finally found an outdoor pace that felt good & pretty easy, and I could keep up pretty consistently--my mile splits were 14:14, 14:22, 14:16, 14:05, and 14:04. Also, the Garmin gave me an "improving aerobic fitness" score instead of "over-reaching" like it did on Sunday, and gave me a recovery time of 28 hours (Sunday's recovery time given was a whopping 69). So that's all encouraging, as I definitely don't want to be overdoing things!!
The surprising thing is that the Garmin is still giving me the same low VO2 max of 34, telling me my "fitness age" is 47 (actual age is 48) and that I'm in the bottom 50% of people my age and gender. I didn't expect that at all, since I'm generally healthy, was moderately active well before I started running, I eat well, and am within my ideal weight range for my height, etc. I guess I'll look at the bright side and say that at least that means there's lots of room for improvement!
If I were to take your Galloway mile you did earlier (10:49) and inputted into an estimate, I would actually get a VO2peak of 24.0.
This would estimate your 5k time around 36:50. Ignore the HR data since I didn't know your inputs. More importantly at this moment, it says that a pace you should find very easy should be around a 14:20-15:15. Which given the 5 miler you completed seems relatively close. But certainly, don't fret. The VDOT (or VO2peak or VO2max) depending on what you want to call it, can certainly be improved. I guarantee as you continue to train you will see that number improve with good aerobic training, mixed with speed work when you're ready for it, and losing bad weight.
This is the chart of someone with a VO2max of 34:
I think most research puts the VO2max value at about a 15-20% improvement cap. But I think that's related to an absolute VO2max which "removes" the body weight component per se. So for example, let's say someone had a body weight of 200 pounds and a VDOT of 30. Their absolute VO2max is 2.7 liters/min. Now let's say that person was able to drop 25 pounds of bad weight down to 175, but didn't actually improve their cardiovascular fitness per se. So at the same 2.7 liters/min absolute VO2max but now at 175 pounds, their VO2max would be 34.3. So they improved their VO2max by 14.3% just by dropping 25 pounds of bad weight. That's the difference between a 30:40 5k (VDOT 30) and 27:25 5k (VDOT 34.3). Now in theory, they could still improve their absolute VO2max by 15-20% max. So they're 2.7 liters/min could be as high as 3.24 liters/min (somewhere around a VDOT of 36.6 or a 26:00 5k vs the original 30:40 5k). Now add in losing 25 pounds for this person, and suddenly their 30:40 5k becomes a 23:10 5k. So it goes to show that there can be a tremendous improvement through continued exercise and bad weight loss to this estimated VDOT value.
I'd guess when I was in Middle School my VDOT was around 38.3 (based on 7:20 mile time). I'd guess my VDOT when I first started running as an adult was around 30.8 (based on 30 min 5k). I'd guess my VDOT after 6 years of training and dropping about 40 pounds from when I started running peaked around a VDOT of 53 in Jan 2018 (based on a 39:54 10k). So my VDOT has improved from 30.8 to 53 (or about +72%) with training and losing some bad weight. I don't add this to brag, but simply to show a real life example of how it can be possible to improve this value fairly dramatically.
My guess on the current VO2max Garmin estimate is that your watch may still need some more data to be more accurate (plus you're still coming off that sickness). Additionally, the HR max you have inputted might be too high relative to your own personal max. What do you have as your maxHR and how did you come to that number?
Something else you may be looking at is the race predictor, but I'd knock some time off those predictions because they assume absolute perfection with running economy which very very few people have. My times usually end up about 4 VO2max values less than what my watch thinks I could do. Here's a chart with lots of different VO2max Garmin race predictor values:
https://cicerunner.wordpress.com/2014/07/11/garmin-fr620-race-times-from-vo2-max/