If I had to recommend one tool I would say use Dovetail. It's a tool done for exactly this that will be super helpful to go from interview notes to insights. And it has a free version.

Dovetail is just one of the tools that does this, you'll find all my bookmarks about such tools here.

For my own research in the last years I've been working with a custom Notion setup. If you are very nerdy this is a really fun way to build exactly the research and analysis tool you want.

By working within Notion I can go from interview notes to in the end have a full report without having to switch tool. Which is pretty awesome.

With notion I can also very simply format reports that don't overwhelm people but still give the opportunity to the curious ones to discover all the quotes that support or contradict an insight.

With the notion databases and formulas I can show what insights are linked to each other and then also do some math to automatically score the quality of my insights by showing in one number how many different people expressed an idea, how many different desk research material expressed an idea, etc.

Check out all the questions about the tools, apps and methods used in Service Design.