I’m somewhat sympathetic to @Jakub_Trybowski’s approach, but moving back and forth between Inkscape and Affinity Designer sounds awkward. I have Inkscape installed on my Macintosh but haven’t used it for much of anything. It tends to crash quite a bit, and since it doesn’t support CMYK, I have little use for it.
I agree with the others about the potential problems associated with opening files from one application in another as part of a routine workflow. Paying attention to industry standards is also situationally important.
However, graphic formats do exist that are standardized and non-proprietary. Inkscape saves to one of them: SVG, which the W3C developed as an open standard. Of course, there’s no guarantee that Inkscape adheres to that standard or that Adobe or Affinity honors it when opening SVG files.
The usual way to save from Affinity to Illustrator is a real hack — saving to PDF, then changing the file extension from .pdf to .ai, but it does seem to work, albeit with all the dangers that would make me shy away from it. I might do that in a pinch (just as I might extract a sponsor logo from a PDF using Illustrator in a pinch), but I’d never hand off a PDF-saved Affinity file to a client and pass it off as an Illustrator file without thoroughly checking it out for problems in Illustrator. For that matter, even then, I’d try to avoid it.
In addition, if I remember correctly, Jakub’s specialty is logo design. Logos are simple enough compositions (at least they should be) that moving back and forth between Affinity Designer and Inkscape seems unlikely to create issues beyond the CMYK limitations of Inkscape. I’d be very hesitant to use this workflow for anything more complicated, such as a brochure or complicated illustration with lots of masks, layers, transparencies, and various effects.
As for Inkscape having essential features that Affinity Designer lacks, I’m curious about what they might be since my overall impression of Affinity Designer is that it’s pretty good. Given that I can barely get Inkscape to run on my Mac, I’ve still assumed it was cobbled-together open-source junk written by an assortment of amateurs. Then again, maybe it’s improved enormously since I formed my opinions about it ten or 15 years ago.