Hey Brian, sorry to hear about your situation...

For sure I would say there are always some challenging times during your job-searching. We always say one should apply for at least 50-60 grad programmes if you really wish to be a MT, same theory applies to internships. It is so normal to be rejected by dozens of employers....

But getting back to the topic of "if running a startup makes you less attractive to employers", I guess the factor should not be a hardcore hindering factor alone. I would say in general it may somehow bring some more considerations to HRs, but may not cause you to get a direct "no" from employers. Or in another way, I should say it will attract only a very few numbers of employers which explicitly express they want entrepreneurs (for sure everyone will think of New World Group). You may wish to dig out if there are any keywords in those job ads to distinguish whether the employers welcome entrepreneurs, eg "intrapreneurship" and "growth mindset", and you may also want to further rephrase your exp in your startup into sth "how your startup exp paved your way into your career goal in 5 years", instead of mentioning how you grow your startup in 5 years.

This can be a very deep discussion, as there are no definite answers even from the perspective of HR. But one thing I am quite sure is that, HR may not wish to see to hire someone who is less stable, as it may affect 2 of their KPIs- Turnover rate & Acceptance Rate...

我都有similar situation 但 so far 都冇話對我proceed interview stages 有啲咩大嘅影響。我個人覺得都係睇你點樣包裝你個答案，例如你可以emphasis 你喺Start-up take嘅leadership roles, gain exposures/ networks or 贏過嘅比賽/獎項。最重要係show 比HR / hiring manager 睇你真係有興趣喺apply嗰間公司度長遠發展 rather than prioritise Start-up。你都可以講吓你Start-up business 嘅 vision, value 點樣呼應apply嗰間公司，而呢個經驗又點樣可以幫助到你add-value to 呢間公司。 

純粹個人分享，希望可以幫到你 :)