I want to make sure we are talking about the same thing here. There is the NASDAQ composite, which tracks all companies listed on the NASDAQ. I’ve never come across a reason to use that for anything that I recall, and I don’t have the .COMP symbol on my screen.
The Nasdaq 100 is different. That covers the 100 largest non-financial stocks listed on the Nasdaq (Technically there are over 100 stocks because some companies have 2 share classes, like Google GOOG and GOOGL)
That index is quite widely followed and traded and the ETF is very liquid. That’s probably the one your referring to. If you want to be long tech do this one and if you want broader you do the Russell or move down to the midcaps even. Diversifying away from QQQ to the SPY won’t do a heck of a lot. It will do some, but better somewhere else.