syncing and editing bookmarks

See the article If your iCloud or Safari bookmarks aren’t syncing - Apple Support

Turn off iCloud Bookmarks and turn it back on

1. Tap Settings > [your name] > iCloud.
2. Turn off Safari. 
3. You can choose Delete from My [device] if your data exists on one or more of your computers. Otherwise, choose Keep on My [device].
4. Wait a few minutes, then turn on Safari again.

Restart your device

Restart your device. If you're not sure how to do this, follow these steps.

• iPhone 
• iPad 
• iPod touch

Mac

After each step, check to see if the issue still exists.

Turn on iCloud Bookmarks and upgrade your software

• Choose Apple menu  > System Preferences. If you're using macOS Catalina, click Apple ID. Click iCloud, then select Safari.
• Install the latest software updates for your device, then make sure that it meets the iCloud system requirements.

Check your Internet connection

1. Quit Safari, then re-open Safari.
2. Try to go to www.apple.com in Safari. If you can't connect to the Internet, your iCloud Bookmarks and Reading List won't update in the Safari app. Get help with your Internet connection.
3. Open a secure website from your Mac to see if you can access ports 80 and 443. Safari requires access to port 443 to push updates between iCloud and your devices.

Check your account details 

Choose Apple menu , and click iCloud. Make sure that you're signed in with the same Apple ID that you're using on your other supported devices.

Turn off iCloud Bookmarks and turn it back on

1. Quit Safari.
2. Choose Apple menu  > System Preferences. If you're using macOS Catalina, click Apple ID. Click iCloud.
3. Deselect Safari.
4. Close System Preferences and wait about a minute.
5. Open System Preferences and click iCloud.
6. Select Safari.
7. Open Safari.

Restart your computer

Restart your computer and see if the issue still exists.

Note : when Mac and other devices like iPhone / iPad are signed in with same Apple ID and password on the same network , book marks starts syncing , it will take time when large number of bookmarks are in icloud , if you turn off bookmark from Mac , it will stop syncing and then you edit and delete bookmarks .

Again when you turn on bookmarks box the same process starts , and the other bookmarks that are not synced will start syncing .

To avoid this let them completely synced and then edit / delete bookmarks .

See the article .

Limits for iCloud Contacts, Calendars, Reminders, Bookmarks, and Maps - Apple Support