With taproot, a number of longstanding BIPs were merged into the Bitcoin standard client/consensus protocol - BIP341, BIP340, and BIP342.
Bitcoin Core is an implementation of the Bitcoin protocol. It is considered by many as the reference implementation and is certainly the dominant implementation on the network at the time of writing.
According to BIP 2 a BIP can be in a FINAL/ACTIVE state. But this does not necessarily mean that a BIP is adopted in Bitcoin Core. Some BIPs (e.g. BIP 39) are proposed standards documents that have been implemented in the wider ecosystem but have not been implemented in Bitcoin Core.
There are three types of BIPs (Process, Informational, Standard) and even within say Standard BIPs they can vary from Consensus (soft fork) to Applications that may not be applicable to Bitcoin Core. BIP 340-342 were examples of Consensus (soft fork). Obviously Bitcoin Core needed to implement these features for these consensus changes to be activated on the network.
However, the state of each BIP isn't always up to date. For example Signet has been implemented in Bitcoin Core but is still in a Proposed state. So any count of BIPs in a FINAL/ACTIVE state wouldn't be an accurate representation of what has been "adopted" or "merged into the standard client".