Have you noticed the rise of paid newsletters? Some are being monetised by platforms like Substack (and even Skool) where people pay for a subscription.
Others are being monetised by sponsorships. I have done 2 so far myself, plus 2 more in the pipeline.
I've recently discovered a platform called Passionfroot which honestly, I'm still trying to work out what it is exactly... But I *think* it's a place for creators to advertise sponsorship spots in their newsletters.
I also just received an email from Destini Copp about a new app https://newsletterprofit.club where you can list your newsletter to connect with other creators to collaborate on newsletter sponsorship and more. Have you explored newsletter sponsorships as a collaboration mechanism? Would you like me to debrief my experience with newsletter sponsorships?