Thank you a ton Noctibur and Pugsy - you have no idea how reassuring it feels to have someone non related to me validate that something is very off with my sleeping - even if the cause is yet unknown

I've been through so much medical gaslighting that I am sometimes really close to depression.
Did he do a physical exam and identify the areas that could be responsible for the snoring?
The ENT doctor did do a physical exam - there is nothing wrong with my septum or airway passages. The symptoms I have are from as from as early I can remember (childhood basically, I don't remember not having it) so I went through removal of turbinates twice - currently I have so big passage that one can push objects of a width of a pen straight to my throat. He said that the second procedure overdone it and one can not do anything to reverse it. He said that sometimes that tissue grows a bit back by itself but because those procedures were done so many years ago this is highly unlikely now. My nose skin collapses completely and closes when I breathe very hard and he said there is nothing that helps that apart from nose trips, but I already tried that and that was useless, they are too flexible and the skin still collapses. He was adamant that no surgical procedure offered will help it. But the again my symptoms where for years before that started to happen so this is not the cause of it (although probably does not help now). He was not concerned about snoring to be honest - he said that most people snore and there is nothing to be done with it. He only referred me back to GP because i started crying, he was quite happy to see me out the door with no further steps to follow. In fact he already discharged be me from hospital outpatient ENT care.
BTW, "spikes" are often artifact and should be ignored (that includes those snoring spikes).
Those spikes are most likely correct. When I sleep with someone in the same room they also confirm that I do not snore constantly, more of heavy breathe/quiet snore and then there is sudden very loud snore sound that gets me jolted up immediately. I can hear this snoring sound while waking up too, and it is on the way trying breathing in, it is basically gasping for air - the closest I can describe it is the sound that a pig makes when excited, definitely much much louder than 40db. Once person jumped out of the bed getting seriously scared because this is really loud from relatively quiet in comparison heavy breathing/quiet snoring. The spike in heart beat at this time is probably also correct too as I wake up dead scared due to sudden loud noise.
Assess your apparent low aerobic threshold
In terms of what causes my lack of ability of exercising I have no idea. General Practice (GP) doctors seem to be disinterested finding out as many things they proposed did not help. Steroid sprays, non steroid sprays, blue and brown inhalers, wearing nasal strips while exercising, controlled air temperature (like exercising inside gym rather than outside) - nothing helps. It seems cardio in colder temperature is a bit better but this is matter of me gasping for air maybe 2-3 min later than in warmer air. They tested me for almost anything allergen wise and nothing really came up. Nowdays I usually get dismissive attitude, probably they are thinking I made with it through my life so far then I can do with it for a bit longer (I definitely get that impression). I start profusely sweating too when I start any cardio, although not so much with cycling (more like a normal person) - there must be something different about that one type of exercise, but I haven't figured what yet. I recently started to ponder if this is to do with my upper body being more or less in the same position - weights and cycling do not move my torso much. I will ask GP to refer me for some cardiopulmonary exercise testing as advised, they may not offer that, but I am not a rich person so going through GP is more realistic for me as this is free in UK.
Theoretically, a HR graph should be an almost straight line with a gradual decline over the night.
However, you have so many HR events packed together you have a bar instead of a line. Again, dozens to hundreds.
That makes me really worried now, looking at my graph it seems i have handful of instances where the amplitude was less than 6... this is all over the place, with differences of 20 doing most of the "bar" shape.
In order to accurately assess that you have to get the actual WatchPAT file and upload to a third part server.
I am not sure if I can get the WathPat file - I will ask the ENT department and if that won't help, use freedom of information act. Not sure if they are keeping those files after someone doing report evaluation. I think I still have an app on my phone for it and watch like device itself - would that be any useful in obtaining that file?
Today is Saturday so I can not do much, on Monday we have a national day off in UK - I will call my Medical Surgery on Tuesday to book GP appointment and ask for both nocturnal polysomnogram and cardiopulmonary exercise testing. Sound like a really good advice on the way forward.