OH 2.5 on raspberry and OH 3.0 on PC

Is it possible to install OH 3.0 on a win10 PC to try it out an still open the OH 2.5 raspberry dashboard on that PC?
On the first try I could not open the OH 2.5 dashbord anymore and restored the PC with a backup.

You can use the remoteopenhab binding to get the OH2 Items available for linking in OH3. That could permit you to set up Items, UI, and Rules in OH3. I assume you plan on running OH3 on the PC eventually?

Your PC and RPi are different devices with different ip addresses
You should be able to access both the pi and pc web ui based on those two ip addresses from any device ( including the pc).
Just use the ip and not localhost.