I save the next stuff into Notion and then sleep on it. If I can't stop thinking about it 3 days later then I just go and do it.
I think discipline is key here. I tend to put time on the calendar for something that I want to do, like writing in my journal, for example. Perhaps you can treat it as a task that needs to be done, rather than another idea you'd like to pursue.
What you want to avoid is thinking about it while doing your current project as @pugson said.
Maybe bubbling with new ideas is a good thing.. especially if the new idea sells to the same customer as your current project. Example: WIP/Beta list .. Nomad list / Remote OK from this community. This is an old article but has aged well.. it lists the benefits of using side projects as a marketing tool medium.com/swlh/side-product-…
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