Problem
After updating WordPress to 6.1, I had an issue where I couldn’t add more than one item per list block in the block editor (Gutenberg). When pressing the Enter key to add a new item, nothing happened.
Solution
I found this solution which was kindly shared on WordPress Support, and it worked for me.
As of WordPress 6.1, this issue appears to occur when using the allowed_block_types_all filter (in my case, in a custom theme). This filter allows you to define which block types are allowed.
If you do use this filter and run into the same issue, make sure that both core/list and core/list-item are included in this array of allowed blocks.
Originally I only had core/list. Adding also core/list-item solved this problem for me.