Updated to Safari 13 and now WhatsApp Web won´t work :(

Did the link you posted make it work?

Are you running any anti - virus programs? Using a VPN?

Try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account 

Safe Mode - About

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply.        Pastebin

Etrecheck – System Information

If this is on your iPhone, open the WhatsApp application and follow the instructions on this link to take another pix of the QR code with your camera. It may help you update with a compatible iOS Safari extension.

There is no WhatsApp extension in the Mac App Store listed among the available Safari extensions. If there ever was, WhatsApp is slow providing a compatible Safari extension. It has been over a year since Apple introduced the new format to developers for the Safari extension.

Today, after signing out and in again, it started to work without crashing.

You are welcome.