You can only get light blocks via the /give command so, er, don't expect to go mining for light. (If you need more details on Minecraft console commands, you can follow that link.) ...

Introduced in Minecraft 1.17, light blocks are invisible items that produce light levels ranging from zero to 15.

Players interested in automating their commands in Minecraft will have to use Command Blocks, but they’ll need to update their settings to add them into the game.

You can get a command block in your Minecraft Java or Bedrock world using cheats and a special chat command.