If someone does a short squeeze of a single company, then everyone who is short that company has a big problem. Someone who is short an ETF that includes that stock is going to also have a problem, but the problem will be attenuated by the fact that the stock is, for a well-diversified ETF, only a small part of the ETF. To get the full effect of a short squeeze, every stock in the ETF has to be squeezed.
To make Bob Baerker's answer a bit more explicit, part of the mechanism of an ETF is that there are entities called "Authorized Participants" that are allowed to create new units of the ETF by buying up the stocks that the ETF represents, and bundling them into the ETF. If there's a short squeeze on the ETF, that would raise the price of the ETF, and then the Authorized Participants would have an incentive to issue more units. If there is a short squeeze on one of those stocks, then the APs would have to pay a lot to buy that stock to make more units, so this can still be a problem, but as I said before, if the stock is only a small part of the ETF, then this increased price will only be a small increase, percentage wise, in the price of the ETF.
So shorting ETFs is more safe than shorting individual stocks, but one should still look at what's in the ETF to make sure there aren't underlying stocks that are vulnerable to short squeezes. And it's not just short squeezes that are an issue; when shorting in general, one should be careful about shorting things with high volatility, and ETFs generally have lower volatility than individual stocks, and so are safer to short.