SD card from a camera no images on iPhone

Maybe your camera does not properly support DCIM spec?

I tested this on iPadOS 18.5 and it works OK even if I create a USB thumb drive mimicking a camera card (*) from scratch:

Format as FAT (MBR)

disk name "NO NAME" and folder structure and file names:

DCIM

100MEDIA

DJI_0628.JPG

DJI_0629.HEIC

DJI_0630.MP4

DJI_0630.M4V

DJI_0631.MOV

etc

When inserted to the iPad, Photos sees that thumb drive as DEVICES > NO NAME and offers to Import files from it and does that successfully.

Or open Files.app and navigate to that thumb drive, select files, Share > Copy and those files are copied to Photos.

And to delete: in Files.app swipe to the left to delete files. Or long-press that thumb drive > Erase and erase as MS-DOS (FAT), ExFAT or APFS (I prefer to erase in the camera because it best knows what it supports).

(*) The file system of an appropriately formatted devics -- for example, an SD card plugged into a digital camera -- must be FAT12, FAT16, FAT32, or exFAT. Media with 2 GB or larger of space must be formatted with FAT32 or exFAT.

The DCIM directory can -- and usually does -- contain multiple subdirectories. The subdirectories each consist of a unique three-digit number -- from 100 to 999 -- and five alphanumeric characters. The alphanumeric characters aren't important, and each camera maker is free to choose their own.

Inside each subdirectory are the image files themselves, which represent the photos you take. Each image file's name starts with a four-digit alphanumberic code -- which can be anything the camera maker wants -- followed by a four digit number. For example, you'll often see files named DSC_0001.jpg, DSC_0002.jpg, and so on. The code doesn't really matter, but it's consistent to ensure the photos you take are displayed in the order you took them.

You may also see .THM files that represent the metadata for files other than JPG images. For example, let's say you took a video with your digital camera and it was stored as a .MP4 file. You'll see a DSC_0001.MP4 file and a DSC_0001.THM file. The MP4 file is the video itself, while the .THM file contains a thumbnail and other metadata. This is used by the camera to display information about the video without loading it.

https://www.howtogeek.com/204228/why-does-every-camera-put-photos-in-a-dcim-folder/

TovaTec – MERA Dive Light & Built In Camera

CAMERA

Video resolution : 1920*1080p 60fps

Photo resolution : 4 MP

Photo resolution : 4 MP

Photo format : JPG

Video Stabilization : Yes

Storage : One 2GB-64GB card

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So the still photos do not appear to be in some Raw format. I'm not sure what format the videos are in.

I don't know how you are formatting memory cards now. There doesn't seem to be a way of doing it "in-camera". Instead of using Disk Utility on a Mac, you may want to use the SD Association – SD Memory Card Formatter for Windows/Mac .

Note that if you allow a very large number of photos to build up on a card, it may take some time before an iPhone changes its tune from "No photos to import" to showing the photos. Or so the thread "No photos to import" when using Lightnin… - Apple Community suggests.

What computer, make, model and year, do you have?

How are you connecting the memory card directly to the iPhone?

What camera is the memory card from: make and model?

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac - assuming you have a Mac?

Please read the following user tip and restate your question/problem in detail including answers to the questions above: 

     Writing an Effective Apple Support Communities Question - Apple Community

Have you contacted Customer Support for the card reader and see what they have to say?

That is a very unique setup and I wonder if anyone here has any experience with it. Do they have a support group at the developer's site?