Heatmap with custom space

{"timestamp": "2021-03-31T14:07:50.465", "key": "h", "code": "4", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:50.592", "key": "e", "code": "14", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:50.697", "key": "a", "code": "0", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:50.801", "key": "t", "code": "17", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:50.960", "key": "m", "code": "46", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:51.089", "key": "a", "code": "0", "type": "[down]"}
{"timestamp": "2021-03-31T14:07:51.169", "key": "p", "code": "35", "type": "[down]"}

Is it possible to overlay this kind of log as a heatmap over a keyboard map?

There is no out of the box way to display an image behind a heatmap.

You could try to create a vega visualization.

Another option would be to do this in maps. You can follow this blog post that does something similar and shows shots on goal overlaid on a ice-hockey rink.