Taproot is a soft fork that activated at block 709,632 in November 2021. It is defined in BIP340–342.
It added schnorr signatures. These let several signers combine their keys into one, for example with MuSig2. Complex spending conditions can be hidden in a tree, so only the branch you actually use is revealed. A cooperative multisig spend looks like a normal single-key payment.
Takeaway: Taproot made advanced uses cheaper and more private without changing the supply or old coins.