There is also "what polls directly measure" and "what we infer from them". Besides the usual adjustments for likely voter models, we also do things like infer

There is also "what polls directly measure" and "what we infer from them". Besides the usual adjustments for likely voter models, we also do things like infer how people will vote in House and Senate elections based on Presidential polling, because we do a lot more Presidential polling than down ballot, because money. So one early thing that seems to have happened this year (and again, we are still early in the process to be making final verdicts in "what happened" retrospectives) is that people split their ballot more than anticipated, which means that the inferences we were making about down ballot races based on Presidential performance were off. So not quite a polling error, but an example of uncertainty that may not have been correctly taken into account in forecasting.