It's not a question of belief, it's an issue of presentation.

Here is what you wrote: "Sunshine is horrible (and other environmental issues)." That is not saying "I have medical issues", it's saying (wrist to forehead) I don't LIKE going out in the SUN!

There are lots of things in life that just flat out suck. There is no way to make worthwhile gains without struggle, effort and dealing with stuff you don't like.

To put my earlier statement a completely different way, you have a choice. On one side is exercise and sweat, on the other side is where you are now. If you are happy the way you are now there is no need to exercise. Otherwise you're going to need to sweat, the choice you then get to make is then a matter of intensity and duration.

Physical exercise causes muscles to use either blood sugar or fat to get the muscles to contract. This is an exothermic reaction causing the muscles to heat up. Exercise sufficient to cause physiological changes causes the muscles to heat up enough to cause sweat. You don't notice this when swimming because it's constantly being washed away.

There is no big red fucking easy button that gets you magic results. There are shorter paths to a solution, depending on your goals (for example if you PURELY want to lose weight you can do things like intermittent fasting, low carb diets and ice baths), but you asked about exercise.

If you have physical issues with sun then the appropriate thing to say is "I have $DISEASE" which prevents me from spending lots of time outside". Being light skinned with a family propensity to Melanoma is not a reason to avoid the sun, being light skinned with a family propensity to Squamous Cell cancer IS a reason to take precautions, especially if that family tendency is towards the cancer going metastatic.

Now that we have more information we can work with something. You don't have to completely avoid the sun, you just have to limit your exposure (duration, clothing) to it and do things to minimize the effects of it (cartinoid consumption, vitamin A with the D etc.). Yes, it takes mountain biking in the Australian Outback off the table, but the sweating issue and your location take that off the table anyway. However the cheapest form of exercise is walking, and if we can somehow dispose of your sweating issues there are walking protocalls that will get you SOME gains, if they're the sort of gains you're looking for (again you haven't stated any goals other than "to exercise", which is vague enough to be meaningless).

There are some diseases that have sweating as a symptom, but it's unlikely you have those. I've spent a lot of time reading about and investigating exercise and diet, but very little on the sweat side of things, mostly because I just accepted that I sweat a lot more than most people given a particular workload. I have a cow-orker who runs ultra-marathons. He is COLD when the temperatures hit ~70 degrees. I wear shorts down into the upper 30s (with a sweater and a hat). He can run in 90-95 degree heat with minimal sweat--he intends to run the badwater at some point--I used to ride a bicycle to work in 0 (f) weather and SWEAT on the way in. This is a normal part of human variability.

Again the issue is how you deal with it. UnderArmour's "Heat Gear" fits close to the body, provides some UV protection and does a decent job of moving the sweat out from your skin. Two or three of these shirts in conjunction with some sweatbands to keep the sweat down on your face and hands and for what is called a "High Intensity Training" or "High Intensity Interval Training" can go a long way towards meeting your goals, whatever they may be.

Realistically though just "man up" and be uncomfortable for 20 minutes 3 times a week. Just going doing that will be a gain in your life.

The Austism thing (I presume from your writing you're down on the functional aspergers end of things) provides a mostly psychological stumbling block. Austists generally have a degree of anxiety about change beyond what normal people face. Examine your feelings about changing your routine, stepping out of your comfort zone and fixing what you may find to be broken.