Web sites load on a PC, but not on a Mac

By far the easiest way to cause poor performance, instability, overheating and crashing is to install ANY third-party speeder-uppers, Cleaners, Optimizers, Virus scanners, Bit Torrent, or a VPN that you installed yourself. 

The idea that a third party, with no special knowledge of the inner workings of MacOS, can somehow find a simple way to protect or speed up 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.

MacOS shares a lot of the lock-down mechanisms developed for the iPhone. Applications are all sand-boxed with a list of the resources they require, and they cannot ask for anything outside their sandbox without crashing. Signed Applications are checked that they are from legitimate Developers, and Notarized Applications are delivered with the assurance that they have NOT been modified since their release by the Developer.

From MacOS 11 Big Sur onward, the system is on a Separate, cryptographically—signed ‘sealed System Volume’. The Mac runs off read-only snapshots of this volume, which is not writeable using ordinary means. Any unauthorized changes to the crypto-signed volume are very quickly detected and you are alerted.

So you could store just about every malware known to mankind on your Mac, and your Mac would not get infected spontaneously. Scanning for virus-like patterns might make you feel a little better now, but non-stop scanning is outdated nonsense, and a tremendous waste of resources.

Nothing can become Executable Unless/Until you supply your Admin password to "make it so".

Effective defenses against malware and ot… - Apple Community

VPN:

A virtual private network, or VPN, is a private connection over the Internet from a device to a specific network.  VPN technology is widely used in corporate environments. If you need to be "present" on an institutional network, a VPN is a great tool for accomplishing this. It is generally issued and controlled by the institution.

Almost all other uses are a SCAM. There is generally no need for you to have a private (and almost always MUCH slower) connection to a VPN vendor's Network, except to make it easier for them to harvest your data to sell. If you are behind a Router you control or Trust, there is NO security advantage whatsoever in using a VPN. Your connections are already encrypted in most cases.

If VPN vendors just stopped there, it would be bad. But many of these packages also insist on scanning all your files, non-stop, -- nominally looking for viruses, but who knows for sure what data they are harvesting. Their non-stop file reading punishes your computer's performance in the process.

Some also break into your other secure connections so they can be FIRST to examine your data, often leaving your Mac MORE vulnerable to attack.

What VPN service to use?

DON'T use VPN services

https://gist.github.com/joepie91/5a9909939e6ce7d09e29

CiscoCrossing wrote:

Example:

Laptops A & B cannot load www.homedepot.ca;

That link does not work ....

try https://www.homedepot.ca/en/home.html

The link www.homedepot.ca; does not work because a semi colon is included at the end of the link.

Try using an "extensions off" window.

Even better, try Rona+ instead.

High Sierra has a very old version of Safari.

Even Monterey does not receive current versions of Safari, but Monterey is enough to run current versions of major third-party browsers such as Firefox.

CiscoCrossing wrote:

Three laptops:

A) Older Macbook Pro running os HighSierra v.10.13.6;

B) Macbook Pro running os Monterey v.12.7.6; and

C) Lenovo running Windows 10 v.22H2

All three laptops are connected to the same network. Laptop A has no extensions, no VPN, no anti-mal/virus applications running. Laptop B has all these.

Both Macs (A & B) will not load certain websites correctly (incomplete image loads and nonfunctioning in-site features such as ‘search’), but Laptop C will open the same site correctly.

Example:

Laptops A & B cannot load www.homedepot.ca; however they can load www.homedepot.com.

Laptop C can load both

I have a 2010 MacBook Air running High Sierra, and a 2015 iMac running Monterey. Both are running the latest available MacOS and none of my Macs have VPN, anti-virus, cleaners etc.

There are some web sites that I noticed don't work properly on the High Sierra laptop; and a few that don't work properly under Monterey. For either, if a site misbehaves under Safari, it almost always works with Firefox or Chrome, however, on these older Macs.

I would also say, your Monterey laptop probably is likely to encounter any number of problems with all those anti-virus, VPN, etc. extra things installed -- all bets are off in that situation.

What you observe makes total sense to me.

My suggestions (which is in line with the people posting earlier): (1) get rid of all those extra things, e.g. security, anti-virus, VPN etc.; and (2) use Firefox and/or Chrome on the older Macs when a site does not work as expected under Safari.