Please help, google cannot fetch my sitemap, tried everything

My website has been up for 6 month, I have 150 url indexed automatically, and google still cannot fetch my sitemap.
I added the path to gsc and it always show "cannot fetch sitemap"

I tried :

- Using template sitemap by google instead of my own

- Putting my sitemap in different path

- Checked using google tool if the sitemap is accessible with robots.txt restriction

- Used xml sitemap checker

- Inspect the sitemap from gsc

- Used plain text list of url instead of xml

- Waited several month

- Submitting my sitemap using full url, and different way to point to the same path

- Added my sitemap full path to robots.txt

Everything is working and should be fine, but I still get this error. I checked my nginx logs and I just never received the request from google bot to fetch my sitemap. I get a requests when I manually use the url inspection tool, but never an automatic request for the sitemap.

What can I do ?