Another Wash Sale question (Sorry)

So the official language says that, you cannot write off capital tax loss if you buy back into the same security or “substantially similar” security within 30 days.

Now let’s say I invested in a 30/70 bond mutual fund, and now I want to buy into a securities only index fund or ETF.

My question is if the mutual fund invested in some similar securities to the index fund but majority of the NAV is based on fixed income bonds, would that count as “substantially similar” security?

I’m guessing not, but I’m no tax expert.