Why has my public IP address changed?

Yes it is a common occurrence and no it should not cause what you are experiencing.

ISPs do not issue static IP Addresses. They can change your public IP Address any time for many reasons.

Did you install a VPN or third party app that claims to protect, clean, etc.?

Post an etrecheck report. It may indicate why you are experiencing slow performance.

Generally, only servers get public IP addresses. A person's everyday computer gets a private IP address, automatically assigned by a "router" which is generally provided by the ISP providing your Internet service.

The changing of an IP address does not break MacOS' handling of passwords for website. It's an entirely different and separate problem.

Are you referring to connecting your laptop to your home's WiFi network or is this at some other location?

Imagine wrote:

Hi DeeperDiver,

For instance, if you go to https://whatismyipaddress.com, you'll see your IP address. My IP changed this morning. I didn't do anything on my end to change the IP address.

What do you think could have happened? Thanks!

Correct. It is showing you the public IP Address assigned by your ISP. These assigned addresses are not static IP Addresses unless of course you are paying for a static IP Address which is unusual for a consumer level account. On your side of your router you have private IP Addresses that your ISP can not change and which are not public.

Imagine wrote:

Thanks Bob. Strange they decided to change it after many years.

Could have been for any reason, they had a glitch, installed new equipment, rebooted a server, decided to mix things up, ...

Ask them if you are that curious. It does not matter though.

What do you think could have happened? Thanks!

Your ISP decided to change it.

Thanks Bob. Strange they decided to change it after many years.

The strange part is it remained static for many years. It is not strange at all that it changed.