I think you can keep some intensity and still be nicer to your knees. After a 20 year layoff due to a career change, I tried one of Barry Ross' conditioning routines (https://www.amazon.com/Underground-Secrets-Faster-Running-Barry/dp/1411657357).
Basically, it's an out and back, but instead of measuring distance, you're goal is to walk as fast as possible for 7.5 minutes, then walk back, making sure you get past your starting point before another 7.5 minutes has passed. That's it. No jogging to cause impact to your knees.
After a couple months, my knees and back stopped hurting, I sat up a little straighter at work, I was more awake, and then I started stairs at work.
You can incorporate many of the exercises in the RR while you're at work. The thing is, you don't have to break a sweat or go full ROM or do multiple sets for there to be a benefit to you.
Try squats and drinking water during your break time. Do balance work (stand on one leg) when you reach for anything lower than your waist. Focus on form over repetition. As your weight continues to drop, your balance points will move and you'll need to work the same balance exercises again. But that's part of the fun; learning where your body is at and what you can do with it!
https://www.amazon.com/Underground-Secrets-Faster-Running-Barry/dp/1411657357
Basic idea: high intensity, short duration of work, big rest between reps
Weight: deadlift heavy keep work under 8 seconds, followed by 3x15m sprints. 3 or 4 minutes rest. 4 sets.
The heavy work recruits fast twitch. Those flame out quickly. Keeping work under 8 seconds avoids lactic events (not the right term). Long rest allows recovery. 4 sets keeps it from being a slog.
Sprints: same thing. Short duration, high intensity, big rest. There's a program from the book, now online (I'll link if there's interest) that shows how to get good target times for the sprints, how to know how many to run since quitting is important.
I got faster - on the clock - in about 6 weeks. My average sprint There's faster than my fastest. I was n beating myself by 1-2m in a 30m sprint.
You cannot replicate the ground forces of sprinting with anything other than sprinting. Uphill sprinting is the same, except that there's more time on the ground contact. (Some angle changes, might not reach top speeds depending on slope, etc).
Stride length will increase with power. Turnover does not change much between a good college sprinter and the elites.
The book also relates to a qb who needed to increase reps at 225 for football tryouts. High intensity, short duration, big rest. 1 or 2 or under 8 seconds work near 1 max rep. Plyos (I did quick set of clap pushups). Big rest. 4 sets. The player went from 2x 225 to (?) in a short time. Raised max 1 rep, which drives up the lower numbers (calculators abound for these conversions which track in real life).
None of these workouts make you sore. So you can lift 3x/week. Sprint a good speed workout.
You don't bulk. Bring as explosive at lower weight will help speed.
My times dropped even mainly doing sprints. When I added weight, they dropped again. My top m/s got boosted which made all running at similar pace use less of my top end speed. This looks like "speed endurance" but is just being faster.
First step improved. Vertical improved. I made a better team at a higher level than I'd previously played. Faster meant easier getting open, defense. But it also meant using less of my max preserving my motor control for throwing, easier to think, see and plan.
It all sounded like bs to me, but the PT who fixed my hamstring, Achilles and knee over a few years told me to try it in off season. It worked.
Because you don't get sore, I was able to sprint / lift 2 or 3 times each between full weekends of play (7-8 1.5 hour games on Sat / Sun - the same the next weekend). Quality speed workouts. Not 70m X 10 like I had done.
Here's the link for the sprints https://www.freelapusa.com/sprint-calculator/
It even has a button to press to populate the fields with a short and long time for an athlete. You can then put in a distance and it calculates target time and intervention time. You sprint the distance. Big rest. Repeat until intervention time is missed. Stop. It might be 4 or it might be 7. If you hit 10, stop and retest. The sprints are done as fly in, to maximize high speed ground contacts which are more valuable than acceleration ground contacts (which have more ground contact time) for this workout.
The workout feels great. Sprinting max feels great. Watching times drop (strength gain, neurological adaptation, "practice") is best. You can't kid the clock.
You can do your own hand timing. I use my timex watch (over my fingers in loose relaxed grip with my thumb to pop the start /split button. My hand timing is very close to what I get with my electronic timer. I tested it so I could just use the watch.
Look in the FAQ for tips, and buy a copy of Starting Strength and read it to learn how to lift and do some basic programming.
Try to separate your strength training and cardio.
Here's some reading for combining strength and running: Strength Training for Endurance Athletes Parts I and II, Endurance Training for Strength Athletes Parts I and II.
There's also Barry Ross's stuff. He wrote a book, too, but I haven't read it.