This is not correct. Taproot does not replace ECDSA but it creates a new address type which utilizes Schnorr signatures.
That's essentially the same thing, the old way is still intact while the new scripts (version 1 SegWit) use the Schnorr signature and drop ECDSA.
Last I heard taproot will replace BTC elliptic curve signatures with schnorr signatures. They claim this will increase bitcoin transaction throughput by 20%
Changing signature algorithm is not the
main reason, the main reason (specially for regular single sig transactions) is dropping the encoding used by ECDSA.
The bigger size reduction is for multi-signature transactions since they will only need a single aggregated signature.
I've been wondering if rumors that crypto ETFs in the united states will be approved in october of 2021 were related to taproots planned rollout in november of 2021.
I don't think so. It is just US that has been resisting ETFs, while they exist elsewhere in the world.
If taproots rollout is delayed or canceled,
That would need a soft-fork because by current consensus Taproot is locked in and must be activated at the predesignated block height.
20% increase in transaction speed
Transaction speed is the same as it has ever was from day 1. I believe you mean transaction size decrease.
Also as I said above the size depends on the scripts, you first have to be using a Taproot script then the size different would depend on the type of it.