Stocks app - does not sync via iCloud

See this Apple document. Use the same Stocks watchlist on your Mac, iPhone, and iPad https://support.apple.com/guide/stocks/stocks-watchlist-mac-iphone-ipad-st60e8b8ef98/mac

You will not be able to see your stocks watchlist on iCloud.com.

I see. The sync process will work only for devices on iCloud with the same Apple ID. Maybe family sharing is what you'd like to use. See these Apple reads on Family Sharing.

Family Sharing - Apple Support

Set up Family Sharing – Apple Support

Leave Family Sharing - Apple Support

Move a child to another group using Family Sharing - Apple Support

Share an iCloud storage plan with your family - Apple SupportS

If you boot into the Safe Mode, will they sync?

Safe Mode - About. https://support.apple.com/en-us/HT201262

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. https://pastebin.com/

Etrecheck – System Information. https://apps.apple.com/app/etrecheck/id1423715984?ls=1&mt=12

Web site version if required. https://etrecheck.com

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.

Isolating an issue by using another user account https://support.apple.com/en-us/HT204443