Is UX research, in a very specialist B2B space with no existing users, possible?

My colleague is working on a project with a client who wants to build a B2B digital product for a very specialist function/sector.

The subject matter is exceptionally specialist/revolutionary so there really aren't any other products out there that deal with the subject or an existing user base.

We want to do discovery work, but i'm really struggling to think of what to do!

Activities we have been able to do;

  • Stakeholder interviews - done
  • Service design blueprint - done (with only stakeholder input)

Activities we want to do but can't*;

  • Competitor analysis - There aren't any!
  • Data analysis (From GA or something similar) - There isn't any as nothing digital yet exists
  • Interviews with existing users - There aren't any
  • Interviews with potential users - Client is resistant to us doing this as they're concerned about IP
  • Usability testing sessions with potential users - Client is resistant to us doing this as they're concerned about IP
  • Survey - no one to send it to/Client is resistant to us doing this as they're concerned about IP

*Please feel free to say "oh but you can, and this is how you should do it..."

Could do;

  • Follow best practices for UI design, UX, interaction design...
  • Do Comparator analysis - For inspiration and ways certain aspects of a digital product can be dine well
  • Test micro aspects of the proposed solution, like form interactions and navigation etc... that don't require domain specific knowledge, with any 'humans' to make sure they are user friendly

Once the product is launched;

  • Implement something like GA so that quantitative data can be gathered
  • Run regular usability testing sessions as soon as there are enough users to do so.
  • Spin up some opportunities for users to provide feedback independently - Forum, feedback surveys, feedback mechanism visibly accessible within the tool, support hotline...

Any suggestions of what we can do to better identify and then meet the potential user needs? Or advice on the things i think aren't possible if you can think of how they would be achievable.

TIA