Power BI Design Best Practices

This is fantastic! I've recnelty been tasked with working on something very similar in my organization. I've approached it through a series of interviews with our report authors, and some othe consistent themes have been:

1. Design to your audience, or as you put it, understand your audience. Figure out who is going to use your report and design around the questions they are going to have and at a technical level appropriate for their consumption. (For example, can you be sure your audience knows that the filter pane exists? Are they going to understand cross filtering? Drill through? If not, don't build a report that relies on those abilities.) On the flip side, they're going to have to join the century of the fruitbat someday, so don't shy away from using advanced techniques, as long as you're using them because you need to, not because they're shiny.
2. Design for the future. Build continuity and handover planning into the earliest phases of your work. Document where your data is coming from, how to update it and how frequently, and any nuances of the report somewhere that it will be easily found and understood. Provide clear comments on your 'code' and your analysis so that you or another analyst can come back to the report in a year and fix whatever inevitably broke. As a colleague of mine once put it, "Your worst coworker is yourself, six months ago. You have no idea what they were thinking and they never respond to emails."
3. It should be clear to you and your user what question you're answering. Heck, put it right there on the report. The answer should also be clear. Consider writing the question and the answer on the report, in text. Plus, that'll help anyone with visual impariments or using a screen reader understand what's going on. (Did you add alt text to all of your visuals? No? Didn't think so.)
4. Speaking of visual impairments, be careful with reds and greens. (As an aside, this is my only critique of your content in the examples for point 5). Around 8% of men and 1% of women have some form of colorblindness, of which the most common is deuteranomaly, or reduced sensitivity to green light (https://www.ncbi.nlm.nih.gov/books/NBK11538/table/ch28kallcolor.T1/). Choose your colors carefully and consider testing them with a colorblindness simulator. Its possible to choose reds and greens that will still look different (especially if they have different saturations) but they won't look red and green, so consider including a key.