JPEG save quality

Photoshop will default to whichever image quality you chose last.

The JPEG save numbers are confusing because you can find at least three different JPEG quality scales in Photoshop and other Adobe photo apps:

• Photoshop Save As/Save a Copy uses the 1–12 scale. 
• Photoshop Export As goes from 1 to 7. 
• Photoshop Save for Web and Camera Raw/Lightroom use a 0% to 100% scale. 

There is a guide to the 0%–100% scale, because how quality changes along it isn’t necessarily linear:

https://regex.info/blog/lightroom-goodies/jpeg-quality

I'm going to answer a question that wasn't asked. Feel free to ignore.

Here goes: saving jpegs at max quality basically defeats the purpose of the jpeg format.

The thing is, "max quality" isn't really max quality. Jpeg compression is always destructive and non-reversible. Every time you resave a jpeg, it degrades a little bit more. The only reason jpeg is still widely used, is that the jpeg compression is extremely effective. It can shrink a file down to 2 - 5 % of native size, with very little visual damage. The key is "very little".

Given that saving as jpeg always destroys the file a little, you may as well go for full payoff in terms of size reduction. The best compromise between file size and data damage is never at max. Going down from 12 to, say, 8, means a huge saving in file size - but still very little direct visual damage. It most likely cannot be distinguished from 12.

The main thing is to never use jpeg for archival purposes. It is for one-time final delivery.

If you want quality 12 to default, regardless of other factors, then create an interactive action with this setting (as the image below indicates with the highlighted "modal control"), or use a script.

If you are re-saving a JPEG that was previously saved (not exported) from Photoshop, then the quality level is stored in the file. The action or script will override the value stored in the file.