MacBook Pro 16'' 2019 CPU at 1GHz for absolutely no reason

The CPU can become throttled at 800MHz (maybe 1GHz) whenever there is a power related issue with the laptop. On some of these Macs everything looks good, but it is still most likely something with the Logic Board causing the problem.

More than likely the Logic Board on this laptop is failing. Unfortunately the Logic Boards on the 2018-2020 Intel Macs tend to have a higher rate of failure, but the MBPro 16" (2019) model seems to be the worst (personal experience and from reading the Apple forums here). In fact many times I don't recommend my organization to repair these 2018 - 2020 Intel Macs as I feel the money is better spent on a newer laptop even though the jury is still out on these Apple Silicon Macs since my organization doesn't have enough of them or had them long enough to judge how the Apple Silicon Macs are holding up yet.

You can try running the Apple Diagnostics, but I find they don't usually detect any issues.

Make sure to disconnect all external devices in case one of them is causing a problem.

I guess you can also try a DFU firmware Revive, or better yet a firmware Restore which resets the T2 security chip & system firmware and the latter erases the internal SSD requiring you to reinstall macOS through Internet Recovery Mode. If the problem still exists after a DFU firmware Restore & reinstallation of macOS, then you have confirmed a hardware issue. Best not to install any third party software and do not restore from a backup while testing the clean install.

How to revive or restore Mac firmware - Apple Support

Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

Have Apple or an Apple Authorized Service Provider examine the laptop to provide you with a repair estimate.

<< Furthermore, the only VPN apps I have are Wireguard and Tailscale. >>

if you are using a VPN to allow your computer to be "present" on an Institutional network, that is a perfectly fine use case. Your institution will support you for any communication problems that occur while using their VPN in that way.

I deliberately called out "A VPN you installed yourself" as problematic, and you responded "you only have TWO."

That it TWO TOO MANY. If a user-installed VPN did ONLY what it said it was going to do, it concentrates your data at the Vendor site, where it is MORE likely to be hacked or harvested for data that can be sold, and several VPN vendors have been caught doing just that, Regardless of their pledges not to sell your data. In addition, several VPN vendors have been caught breaking into secure communication [ineptly] directly on your Mac, leaving your Mac less secure. And it that's not enough, several have been caught installing 'virus scanners' AND scanning your files non-stop (which as I said, punishes performance.)

whether you believe me or not, you can run experiments that prove/disprove. completely uninstall (NOT just turn off) ALL your VPN software and adjust your system settings so NO VPN is being used in any way. Test it that way.

An even simpler experiment to determine whether added software is causing slowness, is to Restart and run in Safe Mode, where no third-party items are loaded.

"Works in Safe Mode, Fails in regular mode" implies, "it's something you added."

Start up your Mac in safe mode - Apple Support

alextruppel wrote:

Thank you for your suggestions. I can assure you that is not the problem. I don't have any anti-virus, cleaner etc apps installed. Furthermore, the only VPN apps I have are Wireguard and Tailscale. And my performance issues are not internet related, so file syncing / backup apps are also not the issue.

Then, you'd have to show your Mac to an authorised service, or a specialist, for it could be a hardware matter.

Poisoning Internet performance:

By far the easiest way to cause poor performance, instability, overheating and crashing is to install ANY third-party speeder-uppers, Cleaners, Optimizers, or Virus scanners. or a VPN that you installed yourself. The main reason is that they are relentless in scanning your files, non-stop, looking for things virus-like patterns in Everything. When completed, they do it all again.

The idea that a third party, with no special knowledge of the inner workings of MacOS, can somehow find a simple way to protect your computer — that is not already being done by MacOS itself — suggests that the MacOS developers are somehow "holding out on you". That is absurd.

You should remove any and all (other than Apple built-in) virus scanners, speeder uppers, optimizers, cleaners, App deleters or VPN packages you installed yourself, or anything of that ilk.

Third-party file Sync-ers such as DropBox, BackBlaze, OneDrive, or GoogleDrive can ruin performance, but are not inherently dangerous.

Effective defenses against malware and ot… - Apple Community

Effective defenses against malware and ot… - Apple Community

System Settings > Login items > delete everything there and reboot.

Before rebooting, get rid of all kinds of 3rd-party modifier apps, antivirus apps, VPNs etc.

Mine is 2018 15" MBP, by the way.

alextruppel wrote:

I'm aware of that. VPN is required because I'm not always in the same location as my own private networks. And this tangent is sidetracking the discussion about the original topic.

Upgrade to Sonoma and see if you have the same problems.

If they persist, show your Mac to a service.

are 'your own networks' co-located where you are? or are they remote?

if you do not need the internet to get there, you could simply manipulate their IP Addresses to have your data Routed over local cabling directly, no Internet and no VPN required.