Here's the full story:
The jpeg file format specification does not support 16 bit depth, layers, transparency or alpha channels.
Stripping these properties to directly save out a jpeg copy - without identifying it as a copy! - was introduced in 2010, in Photoshop CS5.
It had to be removed in 2022 or 2023, because changes in security/file integrity policies in MacOS no longer allowed it.
So Adobe had to introduce Save A Copy, thus making the process fully transparent and up front. The big mistake was that Adobe tried to sell it as a "feature" instead of what it really was: an emergency rescue operation. It should be noted that this is how all other image editing applications have always worked and still work.
Later they were able to find a new workaround, available as "legacy save as": However, it carries some risks, so it is not enabled by default.
If the file complies with the jpeg file format specification - 8 bit depth, no layers/transparency/alpha channels - jpeg is still available under a regular Save As.
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