chess.com Explorer sort of already does this: https://www.chess.com/explorer The default is set to Master Games, but you can use the drop down menu on the right to change it to Your Games and then you can play some moves and see how you score against various openings. This is sort of like your heatmap 
I don't know if there is a way to determine frequency though (other than adding up how many games of that variation there were.
Heatmap of my openings
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Jul 23, 2023
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#2
Ta, that's interesting, and does show frequency. But it's limited to my online games only (useful in its own way) and first 3 moves as a non-Premium user. It's a good start, thanks.
Jul 23, 2023
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#4
CliveHR wrote:
Ta, that's interesting, and does show frequency. But it's limited to my online games only (useful in its own way) and first 3 moves as a non-Premium user. It's a good start, thanks.
Okay sure. I didn't know it was limited (or I knew and forgot) because I had the free chess.com account for many years, but I wouldn't really use the opening explorer back then. Now I have premium (had it for a few years), but I still only check the explorer occasionally since the trends and overall statistics seldom change dramatically because I'm the same player.
I want to create a heat-map of opening lines I've faced in games this season, to get an idea of which are more likely. Any tools out there to help with that? Started a spreadsheet but not convinced it'll show things clearly.