This new major version of hardhat-ethers uses ethers v6 instead of v5. Notice that the name of the plugin has changed too: the previous version was called @nomiclabs/hardhat-ethers but this one is called @nomicfoundation/hardhat-ethers (read this if you wonder why).
Our Toolbox doesn't work with this new version yet, but we'll release a new version that does as soon as possible. If you want to use this plugin in a new project, you'll have to install it, and any other plugin, manually. Also, keep in mind that Typechain's Hardhat plugin doesn't work with this new version yet, but it will soon.
To learn about the changes introduced in ethers v6, read their migration docs.