Hi leonasfar,
Thanks for the reply, and trying those steps, we appreciate it!
Since you were able to pair prior to Catalina, and the macOS Catalina User Guide shows it's still possible, let's do some basic troubleshooting to see if we can resolve this.
First, take a look at this page, which has a few things to look at: If your Apple Remote doesn’t work with Mac
Check the battery as shown, since you were paired previously.
Next, try starting up your Mac in safe mode to test if you can pair that remote: Use safe mode to isolate issues with your Mac
It may take longer to finish the start up, as safe mode does some system checks, and can sometimes resolve issues. You'll also see some differences in the display. This is expected with safe mode, and when you restart normally, they'll be gone.
If you're not able to pair, or see those options in safe mode, try testing with another user. If you don't have one already, you can make a test user. Here's how: How to test an issue in another user account on your Mac
If still no success, I'd recommend contacting Apple Support. Let them know what steps you've already done, and that this worked with macOS Mojave. And quick question, did you unpair the remote prior to upgrading? If not, is the remote no longer working, which is why you needed to try to pair again? I'd let them know the details, if that is the case.
I wish you well!