Opening image in ACR from ScanDisk memory card gets 5+ sec spinning wheel on M1 Max

Have you also seen the delay when using the card from other software? (to see if the problem is Adobe-specific)

What is the speed rating of the card?

Many SD cards — especially the more affordable ones — have transfer rates in the low hundreds of MB/sec or less. This is comparable to a spinning hard drive. And those might not be sustained speeds.

Commonly available external SSDs now reach 500–1000MB/sec, several times faster.

The SSD inside a 16" M1 Max MacBook Pro probably runs in the range of 5000–7000MB/sec, many times faster than external and also up to 30–40x faster than an affordable SD card.

So one possible explanation is the inherent speed limitation of both the SD card and possibly the card reader or Mac card slot that you are using (some pros think the built-in Mac card slot is too slow and they plug in a faster one). SD cards are just not as fast as SSDs, and faster cards might be limited by the reader.

But in the end, regardless of any limitations in card speed or card reader speed, I have to agree with the others: It’s not a best practice to work directly off an SD card. In addition to risking the only copy of a shoot, some cameras are picky about their file system and may not react well to changes made by a different device to a card that the camera formatted. In some cases a camera might decide that card is corrupted, and force you to reformat it. It is always best to copy images to the computer first, and then edit the copies.

I feel compelled to add a 'me too' to the working directly from a pen drive.  It is crazy bad practice and asking for trouble.  I can't bring myself to believe it is still the case, but there was a time when some apps used whatever drive a file was opened from as cache space, which would pretty much stop a system dead in its tracks if you were using an older Pen Drive.

Working directly off a memory card is asking for trouble. Don't do that. There is no reason your operating system should even understand the card's file system, because it was formatted in the camera.

Copy the file properly to disk first. Then you can open it in ACR.

That is working without a net so to speak - what happens if you move your RAW image to local and attempt to open?