I hope those scada systems aren't running on regular Windows. If they are, they should be running on Win10 LTSB on 32-bit so they should keep working till at least 2025 if XP's level of compatibility was good enough to run them.

If they can't be run on that, there's still MS-DOS licenses being sold and FreeDOS might also serve them in a pinch. If a system is not maintained for long enough that it's still running in compatibility mode, you might ask well just disconnect the network cable and run Windows 3.11/95/98. Microsoft is not at fault for the manufacturer not maintaining their systems.

What if the manufacturer doesn't exist anymore?

In that case you either were aware of the risk of your device breaking down in the future and have started looking into migrations or workarounds the moment the news hit, you took the risk that didn't happen and now have to deal with the consequences or you just didn't plan ahead enough.

Just keep running the older version of Windows that worked with the device. Add a couple of layers of configurations, firewalls, VPNs, traffic monitoring and whatnot inbetween to reduce the risk and don't connect the device to the internet. Your solar panel farm doesn't need to access Gmail or run Windows 10.

Your obscure SCADA device is your responsibility. The switchover to 32bit had been announced 20 years ago and the switchover to 64bit 10 years ago.

Also, if the manufacturer doesn't exist anymore, where are you going to source replacement parts?

Or you're using hardware from the 70s that they dropped from software support in the 90s and the software version you need won't run on anything newer than Win2k.

Aren't there still 32-bit versions of Windows 10? AFAIR only the server versions are 64-bit only by now.

Installing 32-bit OS on a 64-bit UEFI system can be a problem.