I haven't done this, but if I was going to, I would target an existing platform that big companies depend on (salesforce, slack, more niche CRM's, etc.) and create a super focused niche plugin that 1) Is not core value prop of the platform, 2) Has little chance of being duplicated by the platform, 3) Has no competition, 4) Solves a real problem companies have.

For example, do research that shows that 7% of companies in industry XYZ use certain CRM. Analyze that industry and see what common use cases and pain points are. Somehow figure out what the CRM is missing for that industry. Validate the idea before building it by reaching out to said companies.

There would be a lot more to it, but basically a plugin for established software a company already uses is much easier and less risk to sell when you are a small shop.