It is maybe comparable to the 1981 attempted coup in Spain - though that is hardly a trivial matter given how it still casts a shadow on politics there four decades on.
Uh, while Francoism certainly still casts a shadow on politics, the 1981 coup doesn't really do that (other than a few people claiming it was a self-coup to reinforce the monarchy).
My go-to comparison would actually be the events in autumn of 2017 in Catalonia, which were compared to a coup by some, the crime is nominally the same as 1/6 (sedition) and what not. And even that is a bit of a flawed comparison as Puigdemont & co. had bigger role directing those events than Trump did organizing the Capitol riot.
