6s / 15.7 / No "Format" option in camera settings!!

You have iPhone 6S with iOS 15.7, read more here...(Extracted from Using HEIF or HEVC media on Apple devices - Apple Support )

Capturing this media

When using iOS 11 or later, the following devices can capture media in HEIF or HEVC format. Other devices can view, edit, or duplicate this media with limitations, if using iOS 11 or later or macOS High Sierra or later.

• iPhone 7 or iPhone 7 Plus or later
• iPad (6th generation) or later
• iPad Air (3rd generation) or later
• iPad mini (5th generation)
• iPad Pro (10.5 inch), iPad Pro (11 inch), and iPad Pro 12.9-inch (2nd generation) or later
• Learn how to identify your iPhone model or iPad model.

Though capturing in HEIF and HEVC format is recommended, you can set these devices to capture media using the older formats, which are more broadly compatible with other devices and operating systems:

1. Go to Settings > Camera.
2. Tap Formats.
3. Tap Most Compatible. This setting is available only on devices that can capture media in HEIF or HEVC format, and only when using iOS 11 or later.
4. All new photos and videos will now use JPEG or H.264 format. To return to using the space-saving HEIF and HEVC formats, choose High Efficiency.

Jeppe11 wrote:

(Old Useless Answer: https://help.apple.com/iphone/11/#/iph263472f78)

Please re-open the link which you have branded as "useless" without reading and understanding it in full.

Please look for these in the same link...

• in the section "Compress photos to save space"
• The part of a para which says "new high-efficiency formats called HEIF and HEVC automatically. "

I am not clear as to what you are looking for. Nor you have shown any picture/screenshot of your device. Merely posting someone else's (rohitfrombuldana) pic does not help.

Here are some pics of my iPhones that may help you understand your device better.