Ventura 13.1 have made Safari extremely slow and partly dysfunctional

After upgrading to Ventura 13.1, Safari has become painfully slow; even sometimes not being able to load web pages at all. Firefox and Chrome do not exhibit the same behaviour. They are lightning fast.

Following the many similar reports and what I could think of, here is what I have tried:

1. Upgraded all software (which seems to be the cause)

2. Remove all extensions

4. Remove all cache, cookies and so forth

5. Reinstall Ventura 13.1

6. Add a new user (standard)

7. Run Safari in safe mode

8. Clean up any unnecessary background processes reported by EtreCheck

9. Removed Safari iCloud sync

10. Remove 'prevent cross tracking' and 'hide my IP address from trackers and websites'

11. Turn off the build in firewall

All of this to no avail.

I'm running on a MacBook Pro, M1, 2020, clean network without any VPN or proxies (again. Firefox and Chrome are unaffected).

I'm pretty sure that I have tried everything; at least what I can think of. So, this smells like a Safari bug. I have noticed two things:

1. When I run network speedtests through the browsers. Safari tends to report approximately the same download speed as when running in Firefox or Chrome; however, sometimes it does not complete the upload test. This is also not an issue in Firefox or Chrome.

2. Normally (pre 13.1 and on my iPad, and iPhone) the start page in safari will show me my favourites, pages from my iPad and pages from my iPhone when synchronising over iCloud. However, only favourites appers when I open Safari on my laptop (this did work pre 13.1).

It is, unsurprisingly highly annoying that I have to migrate to another browsers (this report is written through Firefox). Many of the neat and useful integration of my different devices have more or less disappeared. I'm out of options. I'm guessing Apple's bug hunting team should warm up :)