Not sure if you are looking for feedback for only visuals: But I usually look for the archives to check out at 1 previous issue before deciding if I want to subscribe.

I fully agree with @h_boon. Checking the previous issues is crucial for me to decide whether to subscribe or not.
I'd also make "1300 founders read it" much smaller.

I'd check popular platforms like Substack and others, see their UI, and steal parts from it. I think they put tons of research into making people subscribe.

PS Also, I think you need to add a link to the newsletter in this post :)

Nice domain! Some general feedback from me:

• Make the input type "email" instead of "text"
• Add links to the testimonial author's Twitter
• Looks like you are using quite a few different fonts, font weights, and font sizes; I would make these consistent
• Is this free? If so, then add to copy
• The vertical padding around the error box (e.g. "Email address is invalid") is too big
• The copy under the title doesn't use full stops, which for me makes the page look less legit
• I would have a "Built by @petecodes" somewhere, given you are well known on Twitter!