More Corp Dev Case Questions

I'm in the process for a Corp Dev role for a VC-backed company in the media/tech industry, and I have a case assignment. I wrote a post about it here: https://www.wallstreetoasis.com/forum/corporate/c…. The advice was helpful, and I found and completed an M&A modeling course that gave me a good idea of what I needed to do.
However, all the examples used in the course were on public companies with public financial data. The company gave me their 2021 financials, so I have enough for the acquirer side. My main issue is with the target side. Given the company's stage, they are likely to acquire less mature startups who likely don't have public financials.
How do I account for that in the model, particularly in the pro forma balance sheet and write-up/PPA? I searched the internet high and low, and I can't seem to find a good answer. I'm thinking the solution might be industry benchmarks or public comps, but I'm worried about the latter b/c public companies are more mature, and I might end up overvaluing the target. So hoping someone here might have an idea. Thanks!