Reproduction steps:
Create fig jam board.
Create a few items on the board.
Click and drag to attempt selection rectangle.
Rectangle stops on the first item it interacts with and locks up.
Expected behaviour:
Can select more than one item with selection rectangle.
Using Safari 17.4.1
Hi there! Sorry for the trouble. This looks odd, I tried on Safari 17.4.1 and it works on my end. 
Is it also happening in any other browser (Chrome?) and/or in the desktop app? And do you see the same behaviour in this specific file or any files?
Can you also make sure that the operating system (OS) requirements is minimum macOS 11 or later?
As quick fixes, please try to close any Figma tabs you’re not using, then, in the browser to force-quit and open Figma in a new browser window to see if that helps.
If this doesn’t work, I’d suggest you to reach out to the support team directly via this form for help: https://help.figma.com/hc/en-us/requests/new
Please use your Figma account email, include a link to the file, and share it with support-share@figma.com, so they can take a closer look and try to replicate it.