Login With AJAX still has a legacy widget which can be called in the legacy widget builder, however, this is not actively maintained and will not contain any new features added in version 4.0 and upwards.
Please see our v3 migration guide for information on widget migration into blocks.
Widgets are a term that WordPress has used since its early inception. This is now used interchangably with Blocks or Gutenberg Blocks and will eventually all refer to the same thing.
Login With AJAX supports the block widget builder which was introduced in WordPress 5.8, however, it will eventually be superceded by the Full Site Editor initially introduced in 5.9.
However, these all ultimately are using Gutenberg Blocks, therefore please refer to the block documentation for adding LWA forms to any of these areas.