PS generally remembers the last format you saved with, so if you save something as a jpg the next image you open a file, work on and save should also be saving as a jpg. Provided you are only working on a single layer. If you add layers it will default to psd. One option you have is to set up the Export option under preferences to save as a jpg. Under Preferences choose Export click the drop down and choose jpg, set other preferences as required. You can then use the Quick Export as jpg option under the Export Menu.
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