USB FAT32 Flash drive NOT mountable on M4 MB PRO - Volume shows up in Disk Utility

Thank you for sharing your experience here on the Apple User-to-User support communities.

Readers here are other Users like you, but they seldom go looking for postings like yours.

Unlike some other forums, this is a STRICTLY User-to-User support site. Most Apple employees are prohibited from participating here, except to maintain a friendly, welcoming environment, and try to make certain your post does not go completely un-answered for days.

if you are looking for relief, and none has been volunteered by other Users, the "approved method" is to contact Apple support:

Official Apple Support

Since you chose not to answer my question I'll answer it myself: hoping that Apple "takes action" or "keeping the problem fresh" is an ineffective solution to your concern. It is an unreasonable expectation as well as an inappropriate use of this site.

If Connect and use other storage devices with Mac - Apple Support does not address your concern, then contact Apple Support, here: Official Apple Support. If you already contacted Apple Support, and they could not resolve the problem, and then they recommended that you post a question here because they were out of ideas, then you will need to start from the beginning and describe what you did and what did not work.

Correct, but you did not post a question. There is no question in your original post, nor do I know which conversation you're referring to. Complaining will accomplish exactly nothing. It's a waste of time.

If you want Apple to address an issue, then you need to work with Apple Support directly which involves a numbered ticket. When support runs out of ideas, then it is time to escalate the issue up the support chain where more knowledgeable & technical support teams & engineers can get involved.

Apple engineers & macOS programmers cannot fix any macOS bugs without having real world cases where details & logs are collected to help them reproduce the problem which is the first step to trying to understand & fix the problem. However, people rarely do this so Apple never realizes any issues exist or the scope & severity of any issues. Hoping things will be magically fixed rarely happens.

The USB stick itself could be the problem. Unfortunately the quality of USB sticks is extremely poor even from some name brands. Try using a different brand USB stick to compare results. SanDisk USB sticks tend to be a bit better quality in general.

Also, disconnect all other external devices from the computer just in case one of them is causing a problem.

Just keeping the problem fresh in hopes that apple takes action.

Just how do you expect posting here to accomplish that? Read Connect and use other storage devices with Mac - Apple Support.