Strength Training and my Body Weight over Three Years

Almost 4 years ago, I started strength training. I show in red weekly data for the weight that I was able to deadlift five times in a row (5 rep max).
The blue line is my body weight. It changed between around 74 and 81 kg. I used weekly averages from one to four weighings per week, and I transformed the averages for didactical purposes so that it matches the range my deadlift data. (It is the deviation from 70 kg times ten.)

What did I learn?
At first, I gained a lot of strength and muscle. After the barbell arrived at my basement, it took me 14 weeks to increase the weight I could lift five times from 45 kg to 100 kg. Now I am at 115 kg, so no much gain for the last 3 years. (I also did squats, bench presses and overhead presses, data not shown.)
Along with this gain in muscle, which was visible and obvious, I gained body weight. Shortly after I plateaued at 100 kg, I reached 81 kg, a gain of 4 kg.
But then, slowly but shurely, my body weight dropped. After two years had passed, my Covid infection marked the preliminary low (data gap in the middle). Then two rebounds occurred, but finally my body weight dropped around 3 kilos below the starting weight. But being as strong as I ever was. (Squats, Bench and Overhead Presses show similar developments).
During the whole time, I did not change frequency of training.
My speculation is that I lost a lot of external but also internal fat. I have no data on this, neither a scan or a circumference or a skin fold thickness, just looking in the mirror. Particularly the last drop in body weight might be explained by a change in diet. I ditched almost all freely available carbs as sugar (glucose and fructose), juices and white flour, quit the occasional glass of red wine and instead ate more stringently whole grains and other complex carbs.
Another speculation is that my muscles got more efficient, so my nerves learned to create the required strength with less muscle mass.

What comes to mind when reading this? Any thoughts, comments, questions?

One thing that caught my attention is the pace of change. I’ve seen at least one other weight loss project in which there was no change for months from the intervention, followed by slow steady weight loss for almost a year until there was a plateau at a much more fit level.

Is it possible to add labels for the time dimension on the x-axis?

@Agaricus The x-axis shows calender weeks. At week 35 I had my equipment and could train heavier. At week 14 is the body weight peak just shy of 81 kg. Pretty exactly after a year from this peak the weight loss plateaus for almost 2 years, so there is a similarity to what you were referring to.
Incidentally, it started out as a weight GAIN project, until I realized that body weight is an ambiguous number.

I have been thinking about the decline in my body weight during the last year. I must have created a mild calorie deficit without intending it. What I changed that might have helped here was that I included more fiber into my food, was more conscious of eating more protein, both of which help with satiety. I also became more consistent in a particular eating pattern: First veggies for fiber, then protein, and whenever practical, thirdly carbs. And of carbs much less of metabolically easily available carbs like sugar, white flour, and fructose as in fruits.
I plan to wear a CGM soon, so that I can compare my glucose profiles to the time before I implemented said changes. I hope and assume that my glycemic control has gotten even better because of the changes, which would have helped with fat loss.