It's the "If-you-thought-mercator-distorts-too-much-you-have-seen-nothing" projection.
Joke aside one of the especiall bad things about that basemap is that it isn't actually any projection, it is more some snippets thrown into a pot and then stitched together where it does (or rather doesn't) align.
And the truly horrible aspect about it is that it keeps being used:
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(there are many more examples to be found, including in this thread, if you would dare to seek them)