In testing the Blog (Alternative) Template, I found that only one post was displayed on the front end, even though all my published posts were displayed in the editor.
To replicate
Publish three posts
In Settings > Reading, set "Blog pages show at most" to any number greater than 3
Go to Appearance > Editor > Browse all Templates
Click the Blog (Alternative) template to open it
See three posts are shown in the editor, in the Query Loop block.
In testing the Blog (Alternative) Template, I found that only one post was displayed on the front end, even though all my published posts were displayed in the editor.
To replicate
https://user-images.githubusercontent.com/7662449/194132118-2ebc0bd9-b4c5-4523-9623-0b4fdaaf7b1c.mp4
Result
Visit the front end of the new page you just published. Only the most recent post is displayed.
Expected
I expected to see all three published posts on the front end, as I did in the template editor during step 5 above
Tested with
WordPress 6.1-beta3-54390 Gutenberg 14.2.0 Twenty Twenty-Three downloaded from GitHub approx. 3 hours ago