I'm a longtime Poser user, back to Poser 7.  I have a lot invested in figures, props, etc.  I work primarily on MacOS and prefer to keep everything there since everything works well up through Poser Pro 11.  All my previous migrations to new (Mac OS) Poser versions has gone smoothly.  

I have held off on upgrading to Poser 12 waiting to see if migration of all my existing libraries and work files will go smoothly and will work on Mac OS Big Sur and Monterey.  Also, is product stability and support good now that the product has transitioned to new owners?   I'm still not finding much online information from users about this.

Any information from this community would be appreciated.

You should clearly specify that you are using MAC OS so that you will receive the best advice from those using similar systems.  Everything works fine with P12, the only drawback is if you rely heavily on Python Scripts, you will find that the migration from Python 2 to Python 3 has broken many older scripts.  The possibility of those getting upgraded is, honestly, slim to none.  My recommendation would be to hold onto P11.  I'm on a PC so I can't give you any experienced advice so hopefully, someone with better knowledge will chime in soon.

You can try Poser 12 for free for a short period of time to see if it works for you and upgrading to 12, at least on PCs, does not hamper the previous version of Poser, so you can run 11 and 12 simultaneously.

Sunfire's Creations

If you are having a big investment of models then you might consider to remain on Poser 11 or bellow. There are several reasons, Python combability loss due the upgrade on Poser 12, this will cause that many packages you own and have Python Extension will no longer work correctly, allot of creators were using these for Materials and Morphs. Allot of these Packages are really great and would be of no use in Poser 12.  So if you are a Proud owner of Surreality Packages all or most of these would not work and this is just one of many Artists creations. also most lululee creations would be affected. No need to build up a list as it is Huuge!

The other thing is is that Poser 12 is still on Pre Release . If you would be a New user that just goes for the latest La Femme Products then it could be considered to go for Poser 12 with the restriction to skip older sold products avoiding in desiderable conflicts.

Some superfly materials will also require small adjustments. Firefly materials are unchanged.

I have a ton of content, and I thought the upgrade was well worth it for the quality and speed improvements. However I don't use much python.

If you mainly use Firefly for your renders, I'd stick with Poser 11. The one big advantage of Poser 12 is that Superfly works much faster than in Poser 11. However, they screwed up the material room by removing the simple tab.