Välkommen Malmöhuset! (Sorry if I'm parsing your name wrong -- could mean "bad" something in a Latinate language
Just a quick note about dietary constituents:
Weight changes per se -- dietary constituents aside -- have a huge effect on most biomarkers, so having lost and gained weight complicates comparisons.
Myself, I had (mostly) better numbers on high-fiber, low-fat, non-keto diets than I do now. (But I was younger.)
I now alternate in a complicated pattern of low-fat, very low-calorie ("quasi-fasting"), and high-fat, high-calorie. Two days of the latter, so my average intake is very high in fat (55% or so by calories).
In any event, the interesting test is to try upping the carbs without gaining weight. It could be the weight gain, not the carbs, that you and many here experienced that is the culprit.
On the other hand, there are plenty of other factors. If it's hard to keep your weight from going up on higher carbs, why bother? And, for me, I enjoy my high-fat days (usually two out of three) of macadamia nuts, almonds, pecans, walnuts... (drooling) såååååååå much that I don't care if it increases my cholesterol (and if the research about particle size proves wrong, and that higher overall cholesterol in mid-life really is dangerous, like the older research said, whatever its makeup). There should be more pleasure in life, I'm increasingly feeling. Macadamia nuts are more pleasurable than oats.
Insulin resistance is tricky so I won't comment on that -- tricky, but important.
In any event, welcome.