What is the official explorer and value API for Bitcoin? I am new to cryptocurrency development, and I have noticed that Bitcoin has an official wallet for both Desktop and Mobile (correct me if I am wrong).
My question is, does Bitcoin have an official explorer and value API (such as Bitcoin to fiat conversion) too? If not, are there services or APIs for developers that are recommended and widely used?
I am new to cryptocurrency development, and I have noticed that Bitcoin has an official wallet for both Desktop and Mobile (correct me if I am wrong).

There is no official Bitcoin wallet.

My question is, does Bitcoin have an official explorer and value API (such as Bitcoin to fiat conversion) too?

There is no official Bitcoin explorer or value API.

If not, are there services or APIs for developers that are recommended and widely used?

If using Bitcoin Core, JSON RPC can be used. Example: https://bitcoindev.network/accessing-bitcoins-rpc-service-from-php/
List of RPC commands: https://bitcoincore.org/en/doc/0.21.0/
There are also lot of Bitcoin libraries in different languages which can be used to make things easier:
Scala- Bitcoin-S
.NET- NBitcoin
Open Source block explorers:
https://github.com/Blockstream/esplora
https://github.com/dgarage/NBXplorer