I doubt that you'll find anything that can use the programming/macros from the 850 except for another 700/800/850. The software for the 850 ended back around 2015 and hasn't been updated since. The new CCP software for MX-900 forward won't program the 850 or read the programming.

You can replace the conductive keypad on the 850 to make it work like new:

[Link: p1repair.com]

And here is how to open the MX-850:



You can learn the codes to the 850 from the TV remote. Did you try the discretes I added in the other thread? I'd also take the opportunity to clean the inside while it's apart. 70% or 90% rubbing alcohol will do.