When I got back to my desk computer I found more precise info.

JPG vs JPEG Comparison
JPG and JPEG are often used interchangeably, but they are technically the same format. The difference lies in the file extension’s length, not the image compression or quality.

Historical Context
In the past, some older operating systems (like MS-DOS 8.3 and FAT-16 file systems) had limitations on file name lengths. To accommodate these systems, a three-letter extension “JPG” was used, while four-letter “JPEG” was used for other systems.

Current Situation
Today, most systems can handle four-letter extensions, making “JPEG” the more commonly used and recommended format. However, due to historical reasons and compatibility concerns, both “JPG” and “JPEG” are still widely accepted and used.