In the OP, the cause is that the file name is not correctly quoted i.e. it should be conda env create -f "Python 310.yml"—the quote is needed here because the file name contains a space.

However, this specific error message

SpecNotFound: Invalid name, try the format: user/package

can be raised by a number of reasons.

See conda env create gives confusing message if environment file does not exist and name is given · Issue #11839 · conda/conda (only for old conda versions):

• if you do conda env create -n envname -f missing.yml, then the error message will be seen, while the root cause is missing.yml doesn't exist.
• if you do conda env create -n envname, this is equivalent to conda env create -n envname -f environment.yml, so if environment.yml doesn't exist then you get the same error message.

If you want to create an empty environment, refer to Create empty conda environment . In particular, in certain conda versions, conda create -n envname works, which is likely why many users find the top-voted answer helpful.