Intensity minutes record fine for running and walk activities but not when I choose Bike as an activity from the watch.
Is there a setting I'm missing?
-Thanks

I can't seem to find this option "Is the option Phisio TrueUp enabled or disabled"
Possibly not available for your watch. I see it on GC Mobile (not GC Web!) under the menu of the device (after tapping its icon at the top), in the section General, below Wrist Heart Rate and Auto Upload Activities, and above the time format.
However, if you do not use any secondary Garmin devices, it won't have (most probably) any impact anyway.
Did you try using the indoor cycling activity as I suggested, to see whether it logs the intensity minutes better?
You could also perhpas try starting another outdoor cycling mode instead of the one you use, for example the MTB Activity. You may need to add it with the + symbol, if not listed on the default screen for activities on your watch. If you did not see the Indoor bike activity in your menu, then you can add it in the same way too. Assuming your watch supports all those bike modes.
OK, in that case (if the Move IQ did not solve the problem), you could try starting the Run Outdoor activity instead of Bike. That should help to get the intensity minutes correctly recorded. Once synced, you can then change the type from Run to Bike in GC. Not an ideal solution, but might work, if you do not mind the incovenience.
Looks like a bug in the FR35 bike mode, for some reason suppressing the intensity minutes counting. It is surprising though that the support is not aware of it, and that there are not more users complaining here. Maybe you should look up the topic in the forum dedicated to FR35.
There is another possibility that just came over my mind now - if you did not verify the firmware version of your watch, and do not connect regularly to the watch with Garmin Express over the USB cable, do it now. It will show you the version of the firmware (actually they call it "software version"), and it should be at least Ver. 3.50 (from February 2019). If it is not, make sure to upgrade your watch (through Garmin Express).