Twitter running slowly on Safari?

Go step by step and test.

1. If Safari doesn‘t load a page or webpage items are missing

https://support.apple.com/en-us/HT204098

2. Enable Develop menu and Empty Caches

https://support.apple.com/guide/safari-developer/develop-menu-dev39df999c1/mac

3. If Safari is slow, stops responding, quits unexpectedly, or has other issues

https://support.apple.com/en-us/HT203353

Turnoff or uninstall extensions and test.

Section: Manage extensions: https://support.apple.com/guide/safari/use-safari-extensions-sfri32508/mac

4. Remove cookies and website data.

Manage cookies and website data:

https://support.apple.com/guide/safari/manage-cookies-and-website-data-sfri11471

Try setting up another admin user account 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        Pastebin

Etrecheck – System Information