Hi Timmay,
I’ve experienced similar requests at previous positions. Generally a request for a data dump, as much info as possible across a specified time frame and the requestor has an idea that they can look at all of this granular data to discern a pattern or some sort of relationship.
You mentioned that your CEO said his main purpose is to see sales history so that he can build ideas about forecasting.
What I would do as an analyst if I received this request would entail two parts: 1) the detail he asked for and 2) some highlights summarizing any analysis I performed.
First, I would pull the initial dump and then maybe make a table for the brands and products, perhaps a hierarchy - with summary stats for the current FY and some kind of indicator to show if current stats are in line with history or have increased/decreased.
This hierarchical table could be used as a selector for some line or bar charts to show the trend over time. You could even add filter on the page for the ‘look back’ period - with selectors for last 5, 10, 15 and 20 years.
I might also experiment with the forecasting tool that is included with PowerBI. I think it only works with line charts that have a single series. If your CEO is anything like the CEO at my last organization, he likes “snazzy” things and he did say that he was building ideas about forecasting.
So that is part 1 - it’s pretty much what was asked for with a layout that makes it easier to look at trends over time by brand or product. Maybe even the ability to sort by those measures (sales, units sold… whatever is important to your business - I’m a healthcare analyst so I’m not really sure what people in the sales field are interested in - but you’ll know what your org measures 
).
Part 2 is the the analysis. What I would do is using this charting tool and the summary statistics as a starting point, I would look into the products that have changed to see what’s going on with them. My goal would be to provide the CEO with a higher level summary analysis. Very importantly I want to provide him with statements here - not more questions.
I would want to highlight products or brands with actual changes vs changes that might have been driven by black swan events such as “product X sales have been down compared to historical norms, but that coincided with a drop in production tied to supply chain issues as a result of that tanker stuck in the Suez Canal” or “toilet paper sales increased in FY2020 compared to that last 5 years, but that was primarily driven by panic hoarding in Q2 during the pandemic”.
I would also want to pull out the products or brands that have had changes, compared to (what I would assume would be) the majority that’s just trucking along, business as usual. I would want to filter out the noise of business as usual and special events in able to focus on brands or products with indicators of true change.
These pull-outs/highlighted products might each have a different set of presentation charts. Which you’ll probably be able to select from because you’ve had to use more of these in your analysis.
As others in this thread have mentioned you need to be brief. Hit 'em with the highlights, as one of my managers used to say. And remember, BLUF - Bottom Line Up Front.
You can them give him a super-bullet point summary along with the data dump he requested, but hopefully that data dump is set up in a way that lets him filter and look at details he might be interested in via the hierarchical table with summary stats and the linked trend charts.
FWIW, I’ve been through similar scenarios with new execs numerous times - either because they are new or when I’ve been new to the analyst team. Most of the time I’ve been able to develop a very positive working relationship with them where the exec starts actually talking with me and letting me know more of their ideas and the questions they want to answer.
Data consumers generally haven’t learned how to articulate their questions, and are used to just asking for a data dump. I’ve found that giving them what they’ve asked for (which is always important, I’ve known people to get frustrated when they don’t get what they asked for) as well as some sprinkles of insight work well to move toward a more collaborative analytical partnership.
Sorry this answer was probably a data dump in itself. I hope it’s helpful.