I'll throw in my 2c because I've spent probably at least a hundred hours diving into this exact topic trying to understand exactly what is what. Firs thing is that UTX is a blood lactate measurement and ZoneX is a Hr measurement, as has been stated in this thread already HR isn't a universal thing and not a great measurement in general. Here's a video talking about why Z2 is less effective for a majority of rowers than Z3 unless you're doing absurd amounts of volume and are otherwise overtraining your aerobic system (very unlikely)
https://www.youtube.com/watch?v=QXSIfSocmQc&t=919s. I'd say most of my UT2 work is Z3 and even a good amount in Z4 because of my drift.
Here's a video talking about why HR training also isn't a super great metric compared to RPE:
https://www.youtube.com/watch?v=35kjwW1HAAw
The tl;dr of these videos is that HR is too variable for beginner athletes whose bodies are not accustomed to the load yet, and that rowing is primarily a power-endurance sport (unlike running or cycling) so your goal should be to both maintain a certain blood lactate over time (see: UT2 / UT1 paces based on your 2K time) ie between 1.5-2mmol, as well as develop a powerful stroke. You can't do the former if you go into Z2 because it's probably too light of work unless you're older or very young, your lactate won't be where it needs to be to develop this adaptation. You can't do the latter if you do Z2 for the same reason. Personally it wasn't until like last month after my first 1M meters that my HR aligned to what it says on the Free Spirits HR band calculator - prior to that I have consistently been 20bpm higher, on average.
And finally a video about what UT2 and UT1 should "feel" like
https://www.youtube.com/watch?v=gaZudbfGjmQ
I like this video because it paints a good picture of what both should feel like. He uses the metaphor of a bucket with a hole in the bottom - UT2 should feel like a faucet has been turned on and that water is very easily going out of the hole, no buildup. No feeling of burn at all. UT1 is where the flowing faucet fills up the bucket at the same rate the water flows out of the hole, so right on the threshold of feeling a burn, but still primarily an aerobic workout so if you DO feel a burn, back off a bit.
If you're not already tracking, you can define each pace as a % of your best 2K Watts, which you can estimate if you haven't done one yet through various means. I've made a simple program to take your time and display it based on your 2K split pace, so for example my last tested time was about 7:45 (1:55/500m) which gave me the following:
24M 200lb 67in HR45-205 | 2K 7:45 (June 23) | HM 1:38 (June 23) | First million meters! (Nov 23)