Resident Evil 4 Remake bug affecting progress in Chapter 12 will be patched by Capcom
In the meantime, there are a few steps you can take.
Capcom has warned Resident Evil 4 Remake players of a rather serious but rare bug in Chapter 12 that could stop your game from progressing.
You can keep the bug from triggering, and be sure to have a save handy before starting Chapter 12. The workaround is posted below the video and is as non-spoilery as possible.
According to Capcom, there is a cutscene that will play at the beginning of Chapter 12, after which you will receive a key item. This item is needed to progress, and the bug is activated when you start attacking with your knife. Doing so could keep you from obtaining the needed item.
To keep this from happening, Capcom says not to attack with the knife until the notification for obtaining this item is displayed in the upper right of the screen.
After obtaining the item, it will appear within the Key Items & Treasures menu in Leon's attache case. If it has not shown up, you will need to reload saved data from before the start of Chapter 12.
Capcom said it plans to fix the issue in a future update and apologized for any inconvenience. The good news is if you have encountered the bug after the patch is applied, you can continue the game even with the saved data where the error previously occurred.