Looking at your graphs, you’re tracking averages per month. This could be skewing your perception of improvement. In Intervals, after each ride, you can see your performance for various power/minute lengths versus the season as a whole and all time. You can also hover over each historical number to see what date/ride achieved the max. So, for example, if you want to improve 20 minute or hour power, you could be looking at how you improved during the key sessions, not as an average of all rides per month. You could do 4 easy 90 minute rides and 1 VERY hard one in a week. Do you want to know how you performed for 20 and 60 minutes as an average across those 5 rides, or do you want to know how you performed on the 1 ride where it mattered?
Figure out which goals you have (is it improving 1 minute power? 5 minute? FTP (or 60 minute)?)). Once you know what your goals are, compare individual rides for those power durations.
Note: if you don’t see the duration (or time period) you want in intervals, you can configure what is shown.