LR4 will **probably** not work on Sierra
Owners of old programs simply have problems with Mac El Capitan/Sierra... none of which is Adobe's fault... Adobe did not change your old program to make it stop working... Apple changed their operating system and THAT is why your old programs won't work, not because of anything Adobe did... Also... every time Apple issues an update, there is the risk that an old program that HAS been working will STOP working... bottom line, old programs require a matching old operating system
Thank you for your quick response! That's what I was afraid of. So I guess that means I would need to exports all of the photos to at least ensure that the work I did on them is not totally lost and export the catalogues "just in case." But if I am understanding correctly, the current creative cloud programs should work on Sierra if I upgrade and sign up for the plan? And the LR download from the Creative Suite will open my old catalogues, right?
The most Sierra-compatible versions are Lightroom 6.8 or later, or Lightroom CC 2015.8 or later. Earlier versions have known problems in Sierra. Here's the official word from Adobe:
When you get Lightroom 6 or Lightroom CC 2015, all you have to do is use the new version to open your Lightroom 4 catalog. Lightroom 6/CC 2015 will then convert your Lightroom 4 catalog to the current format. You shouldn't have to export anything, but you still can if you want.
If you need to save space by breaking up your Lightroom 4 catalog, you should do it after converting the single current catalog to Lightroom 6 format. For example, if you break up up one LR4 catalog into 10 LR4 catalogs, you will then have 10 catalog export steps plus 10 LR4 to LR6 catalog conversion steps. You'd probably rather do just one LR4 to LR6 conversion step followed by 10 catalog export steps.