If your Mac can't boot into Safe Mode, you can check whether you were actually in Mac Safe Mode, whether the way to boot your MacBook Pro into Safe Mode is right, and whether your keyboard functions well.
Based on your description, your MacBook Pro should be equipped with an Intel chip, and the steps to boot into Safe Mode are correct as it worked many times before. Then, we can narrow down the possible reasons to these two aspects:
Check if you were actually in Mac Safe Mode
Perhaps, you are already getting into Safe Mode but you think the Mac boots up regularly. If you can't tell the differences between them, you can check in this way:
- From the Apple drop-down menu, select About This Mac.
- Select Software by selecting System Report and then scrolling down.
- On the System Software Overview pane, look at the Boot Mode's status.
Check if your keyboard is functional
Maybe the Shift key is not working on your Mac. You can check this by typing capital letters. If you are using a wireless keyboard, check the Bluetooth connection, the USB ports, and the USB cable, to make sure it works well. Or, change to another healthy keyboard and try to boot Mac into Safe Mode again.