The "emergency fund" general advice does not really exist. It has to be taylored to the situation - if you are a Civil Servant in France, you know that next months salary is comming with 99.9% likelyhood. If you are self-employed cave explorer in Colombia, you know that your next pay may be fantastic, non-existent for a couple of months or anything in between.
So first things first, evaluate your situation and decide what you'd need if things turn bad for a few months, which can be from nearly zero to 6 months salary - which for some is difficult to save.
Still you may decide not to hold cash, but rather near cash equivalents that at least give you some yield, like short term debt, easier in the form of a mutual fund.
There are many investors who live day to day. If we talk about them, they do not depend on their monthly income. If they work every day, they get wages, if they do not work every day, they do not get wages, and many times they do not find work at all. Such people should create an emergency fund by calculating their monthly expenses. For example, how much money is being spent in a month. The best way would be to keep three times their monthly expenses in the emergency fund. Because since they do not have a proper determination of their income. In that case, it would be very good for them to adopt this method.
I think keeping money in cash for the emergency fund is the best way. Because many times it is seen that we need money very urgently. At that time, we do not get money if we keep it in the bank. Again, many times it is seen that our bank account gets locked or damaged. If we need money immediately at that time, we have to take a loan from somewhere at that time and if we do not get a loan, we may have to sell our holdings. I think it's a good idea to keep cash in an emergency fund.