Ann: S&P DJI Announces June 2024 Quarterly Rebalance, page-9

Goldf / Ramsay,
I did a dive to see if gaining new ASX100 membership brings any benefits.

It seems new membership of the ASX200 carries more weight. As motley fool points out;

Investors fret about ASX 200 inclusion (or exclusion) because this is the index that has the most potential to make an impact on a company's share price.For one, the ASX is full of managed funds and exchange-traded funds (ETFs) that track the ASX 200. As such, any fund tracking this index has to hold all of its shares within its portfolio.
This means getting an ASX 200 ticket can be great news for a company's share price.
Further, there are lots of fund managers that actively pick stocks but do so out of the ASX 200 index only. So once again, having your company with this index increases its exposure to professional investors, and raises its profile.

However, the ASX 100 index offers none of these benefits.
There aren't too many fund managers that I'm aware of that only limit themselves to ASX 100 companies.
Further, the ASX 100 index is not one that too many managed funds or ETFs track. In fact, the last ASX ETF that tracked the ASX 100 was wound up back in 2018.