It is the same situation with my programming; I can't work on any of
my projects because I can't stop criticizing my own code
Pseudo-code
The method for roughly scripting functions without bothering with working (much less 'perfect') code, is to write pseudo-code.
Sometimes partial-code, sometimes a brief description, or just placeholders –– whatever creates the bones of the project.
The goal is to create a template of the larger project while excluding the need to judge it on syntax or perfectionism – details that should evolve after the main structure is established.
By metaphor, outlining is the method writers use to create a template without getting hung up on undeveloped narrative voice, rhythm, and tone.
Outlining
You say your problem is 'crippling perfectionism' – not procrastination, and not a lack knowing what to write. I believe you. This is not a 'creative juices' problem.
You might be struggling with the wrong tool-set at this step of writing. Another metaphor: you're holding the thin-hair detail paintbrushes, but what you need first is some broad strokes to define the overall picture.
When I outline, I write in 'pseudo-code'. Some is partial prose, some of it is explanations of what's suppose to happen, and some is just placeholder text to jog my memory later. In other words, there is no format.
If I get lost into the details I could write the same scene for hours and it never go anywhere just wallow in 'tone', so I have learned to step back and place my story beats first, then connect from beat-to-beat.
It's still creative writing of course, but I know what it needs to say.
Snowflake Method
Snowflake Method is similar to outlining in that you know the broad message, but you don't know which key 'beats' need to flesh out.
It works by starting with a very simplified (reductive) single sentence of the topic:
"Sam Altman testified at the US Senate yesterday."
As you add necessary information to this too simple sentence, it will inform you what information needs to expand to create the larger article.
"Sam Altman, the CEO of Open AI, testified before a divided US Senate, advocating a government license for AI developers."
–– Add a paragraph about Open AI, another paragraph about the various viewpoints in Congress, another paragraph about what he said (this is a very simplified explanation). Keep going until the too-simple sentence (and the article) has the relevant information.
Be Utilitarian
Newsletters are not 'creative writing'. You need a practical, utilitarian system that puts structure on the page without activating your perfectionism.
I think it might be especially useful to put unadorned facts on the page, in a logical order, where it's almost impossible to be clever or decorative. It won't prevent you being a perfectionist, but it will prevent perfectionism from blocking the first steps.