Hello! Welcome to Uipath World! hahaha 
When we talk about RPA, In my opinion, there’s nothing that can’t be automated (since it has patterns and are digital). I have faced millions of challenge during my experience with Uipath (3.5 years) and until now none of them was impossible to complete. Of course there are exceptions. For example: It’s impossible to automate a process that uses a physical invoice document (just the part of reading the content from it, but all the rest can be automated.).
1st Tip: First of all, consider a Digital Transformation to the process beeing automated. And then you’ll have the answer if it’s possible to automate or not 
2nd Tip: It’s possible to create Custom Activities for Uipath along your development. So if you doesn’t find anything on the Activities Package, you can create yourself a Custom Package which will do what you need (A barcode reading, for example). Just don’t forget to post on Uipath Gallery to help us too hahaha
3rd Tip: There are systems that is best to automate than others. Example: Local Desktop is easier than Citrix Environment (VDI). But it’s not impossible. A .NET application is easier to automate than a Java Application. But it can be done as well.
4th Tip: Always check the Uipath Community. We are here to help if you have any doubts!
I think that’s it. I’m not the best developer in the world. But I think these tips can help you start this journey. In my opinion, Uipath is the best RPA market. You are in the right path 
Hope it Helps!
Regards,