Your Mac does not have Lightning ports.
iMac (24-inch, 2023, Two ports) - Tech Specs - Apple Support
iMac (24-inch, 2023, Four ports) - Tech Specs - Apple Support
It has two multi-purpose USB-C ports which support
- USB 3.1 Gen 2 (up to 10 Gb/s)
- USB4 (up to 40 Gb/s)
- DisplayPort
- Thunderbolt 3
If it is the four-port version, it has two additional single-purpose USB-C ports which support
- USB 3.1 Gen 2 (up to 10 Gb/s)
Your iMac's Thunderbolt ports might be marked with a lightning-bolt symbol – but Lightning is a different type of port, found mostly on older iPhones, iPads, Magic Keyboards, and Magic Mice.
Apple has a USB-C to SD card reader that would work with your Mac, and there are more USB SDXC card readers on the market than you can shake a stick at. Many these days have USB-C plugs, and even the ones with USB-A plugs can be used with your Mac with the aid of an adapter (like the Apple USB-C to USB adapter).
Some examples: https://www.amazon.com/s?k=usb-c+sdxc+card+reader