It is absolutely not open source.
The "Fair Source" license that n8n invented has two related qualifications that make it not open source:
> You may use or modify the software only for your own internal business purposes or for non-commercial or personal use.
It's not open source if you can't use it professionally or sell work derived from it [ed: comments have correctly called out that this is not the deal, thank you]. There's no chance this license or anything like it is ever going to be an OSI approved open source license. https://opensource.org/licenses