Two questions. The file you are using is definitely called EOSR5150.FIR?
What card are you using to transfer the file from your download device to the camera?
Having same issue. Canon site gave me a file named eosr5-v150-mac.dmg (using macbook) and I placed it on the SD card's root since I saw no stipulation about which to use. I did two downloads....one directly to the SD card and when that did not work on the camera, I downloaded to macbook and then to the SD card, same outcome. Advice?
Once the eosr5-v150-mac.dmg files has been downloaded there are a couple of ways to open it. One is to double click on the file and once your Mac extracts the folder it will show you the PDF folder and .FIR file.
The other option would be to bring up the .dmg file in your Finder and use either the List or Column view. When you click on the .dmg file Finder will show the contents of the file either to the right of the folder or below it.
You will download a self-extracting .ZIP file to your computer that must then be opened in the computer. This produces a folder with a file called EOSR5150.FIR. You copy THAT to your SD card (making sure there are no other such files there) and then update the firmware through the camera's menu system as indicated in the manual.
On A MAC
A DMG file is a mountable disk image used to distribute software to the macOS operating system. The file is typically downloaded from the Internet by a Mac user, then double-clicked to install an application on the computer. So, having downloaded it to your iMac, you need to execute the file ON THE COMPUTER and it will create the .FIR file I referred to. You then copy THAT file to your SD card and it should be recognized by the camera.The other option would be to bring up the .dmg file in your Finder and use either the List or Column view. When you click on the .dmg file Finder will show the contents of the file either to the right of the folder or below it.