Is Hang Seng Tech an index? Which ETF is the best to track this index?

Yup HST is an index. You can refer to this to take a look at its holdings etc: https://www.blackrock.com/hk/en/products/315923...

I personally hold 3067 (HKD market)

Hang Seng TECH Index is an index:

https://www.hsi.com.hk/eng/indexes/all-indexes/...

You may use aastocks.com to search for all HS Tech ETF listed on HKEX:

http://www.aastocks.com/en/stocks/etf/search.as...

And then there is the Lion-OCBC ETF on SGX:

https://portal.iocbc.com/products-and-solutions...

The lowest TER ETF is the iShares 3067 (0.25%). In Jan this year, they announced not making new investments in sanctioned Chinese companies:

https://secure.fundsupermart.com/fsm/article/vi...

But this restriction is lifted in Jun:

https://www.blackrock.com/hk/en/literature/shar...