I had a similar experience. My suggestions are:
- have a clear, simple story to answer "why are you (single person) leaving the startup". You'll be asked at every interview (and if multiple people apply to the same company, you want a coherent answer). Include that you all are leaving if this is the case -- the risk is that you (single person) are seen as one giving up
- list down 4-5 main achievements. Make sure there are 1-2 which are not co-done, but you can state "this was mostly my own achievement". This is the hardest part, but if you're still working together you can easily agree on how to split
- make sure to clearly tell 1 story, which doesn't need to be the one of the startup, but the one for which you're seeking the new job position -- if I'm looking for a position as data scientist I'll focus on my research experience, if I'm looking for devops I'll focus on security, etc.
- in linkedin specifically, if it applies, link some press or some blog post, or anything I could spend time digging in to get to know you more -- if you feel that the list of jobs is not enough, help me finding more info about you
From the other side of the table, when I look for people to source/interview, I look at the total working experience. Wether it's 4y in a single company or 2+2 it doesn't make any difference. I personally (I see others can disagree, but this is me) see as a yellow flag a 1+1+1+1 experience, simply because I fear you'll leave my company after a sole year.
(If you'd like to chat more feel free to ping me via email.)