Heart sensor vs. hairs on the wrist...

You should expect issues with the functionality of the HR sensor.  period.
That may or may not have anything to do with your hair.

the wrist based Optical HR sensors are hit and miss- depending on the person.  I've had a few different watches with HR sensors- and while they work pretty well at rest- using them during an activity is a mess for me.  And- I don't have nearly that level of fur.  maybe it's just the divot in my boney wrist?  I use a separate OHR on my forearm for activities- which works fine.  

so- you really won't know how well (or poorly) it will work until you own it.  

and of course- one swipe with a trimmer- and you can solve the hair problem... if it's a problem.

I wondered this back when I got my first watch, a Fitbit Blaze.  I tried shaving a gap for the HR sensor and seeing if it made any difference to a number of things, mostly how quite a rapid increase in HR would be detected.

It didn't make any difference to me.  I am of course a sample size of exactly 1 and I didn't really do a lot of rigorous testing, so take this reply with a massive dose of scepticism that it deserves!

It won't be your arm hair, it'll be the sensor.  If the heart rate is critical, it's either a different product (Apple Watch is good) or you get a strap (forearm or chest).

Agreed.  I got fed up with the sensor accuracy, so I bought a heartrate strap.  It's so much more accurate. 

It seems like the watch's sensor works ok if you're sitting quietly at a desk or sleeping, but for activities I just can't trust it.  For example, it will often show an absurdly low heart rate sometimes for the first 30-40 minutes of a hike and then suddenly it will kick in and display a reasonable heartrate for the remainder of the activity.

On my wrist it is close to perfect provided that I wear it properly. Meaning 3 cm above ht wrist bone and quite tight.  I do have several hr belts, but it works surprisingly well

well simple answer is that if you do, shave your wrists !!!

Should I expect any issues with the functionality of HR

Watch is based on Fenix 6 so you can expect to have issues with sensor. Not because of hair.

My hair does not create issues with my watch. Coworker had issues with his F6 OHR, he said it was due to his hair. My watch worked fine on his hand and his watch did not work on mine...

So some units may work, others may not. Good luck.

well if you will be using hiking mostly just get away from fenix6 series.

So, it means that depends on the device - some of them works quite well, some not necessary. My wrist shouldn't cause an issue then. As DontGetTheSwiss said, the HR reading issue is related more to the sensor but there's quite a lot posts treating this topic.

I gonna use Tactix Delta as my daily watch, not "medical device" to measure my "health" level in the preventing sense. The activities I do are bike riding, hiking (occasionally) in the nearest mountains, skiing during the winter. It's nice to have the the heart rate measures and follow up any progress in my activities or in my case - rather calories burned. Looking at the other posts, it seems, that I cannot expect brilliant results... I have read about Apple Watch or Suunto, that they're also struggling with HR accuracy.