If you use Dollar Cost Averaging[1] there is no such thing as a good or bad time to buy ETFs. As long as the market goes up on average, which is has done throughout history, then you will win over a sufficiently long horizon. A popular phrase is "It's not about timing the market, but time in the market".
Make sure you research your ETFs and what they are tracking e.g most of the Vanguard ETFs (e.g. VOO, VTI, BND) are quite reliable but if you are investing (and not day trading) avoid leveraged and inverse/short ETFs such as SPXU and TQQQ. They may seem attractive now but they are based on derivative products so their pricing is subject to a number of factors.