Unable to write files to extenal memory (flash drive / SD card)

I understand that any drive you connect to the MBP displays the same inaccurate disk info.

I also understand that these drives are working properly on other Macs. Obv this is unusual.

Are all of these problematic drives FAT32 formatted?

If a simple reboot of your Mac doesn’t fix things, see if the problem still happens in safe mode.

How to use safe mode on your Mac - Apple Support 

Safe mode will often correct weird software behavior by forcing the OS to clear caches, do disk repair and other housekeeping and temporarily disables third-party mods.

Can you access the drive(s) while in Safe mode?

You can exit safe mode by restarting your Mac normally, then reevaluate the problem.

Are these drives connected to your MacBook Pro directly or through a hub/dock?

If you are using a dock then try connecting directly to the Mac using the different available ports. Also, if using a dock and you have other devices connected to the Mac, disconnect the dock and all other devices and see if that makes any difference.

So we don't have to play "20 Questions" here, please run an EtreCheck (free) evaluation of your Mac and post the generated report back here in a reply. EtreCheck is a safe and highly regarded utility from a trusted developer and respected ASC contributor. The diagnostic report will not include any personal info. The utility simply gathers specifics about hardware performance and installed software that might be in conflict with the OS.

Please navigate to EtreCheck.com to download the utility. Be sure to Allow Full Disk Access when you install the app. Once you’ve run the app and created your report please post it with your reply to this message. 

Please note you must upload the full report. To see how, please click >  How to use Add Text when posting… EtreCheck Report.

We’ll use your EtreCheck report to look for the things that may be causing your problem and advise how to correct them.

You're welcome.

I'm happy to see that you you've got this sorted. 🙂

Any device that will not tell Disk Utility its Make&Model, and a reasonable non-zero size/capacity is NOT useable on your Mac.

that report shows a drive capacity of Zero bytes. At a minimum, it needs to be repaired with Disk Utility. if it will not come clean, you need a different drive.

donuan wrote:

Well, the problem does not seem to be with the drive, as this applies to all drives I try to connect to the computer, and these drives all work just fine on other mac computers.

I have also tried reformatting them to no avail.

like I said the problem seems to be with permissions, but I do not know how to solve it.

Tthe Volume shown on the device in your screenshot has a capacity of ZERO Bytes, and contains ZERO bytes of data.

Consider using a device formatted as MacOS extended for Mac-to-Mac transfers, or ExFAT for PC to Mac transfers.