CS3 runs as normal on both Windows 10 and the new Windows 11 machines. I know because I had it installed on both. Here's Adobe's explanation:
Regrettably, we must inform you that Adobe officially announced the discontinuation and end-of-life status for CS3 and earlier legacy products several years ago. As a result, the activation servers for older versions of Acrobat and Creative Suite (CS) applications have been retired. Consequently, without these activation servers, these application will not reactivate on new or same machine. If you still have CS3 product already installed and activated on any device, you can still use them. But they can't be re-activated anymore on new or same devices.
In the past, as a goodwill gesture, we provided free replacement serial numbers for CS3 when Adobe was offering one-time exceptions for CS2 and CS3 users. However, this process has also been discontinued in accordance with our support policies. At this time, we no longer have access to download links, updates, knowledge base articles, tools, or support teams to assist with the activation or installation issues related to these end-of-life products.
Here is the replacement serial number that they provided to me at the time: 1045-1631-8110-5780-1232-7825. Try it and see if that number will work on your machine. If it does, check "Never Register" when prompted.
Note, however, that if you get it to work on your, say Windows 10 machine and you move it to the newer Windows 11 machine, then you can only use it for 30 days until it needs to be activated by Adobe. This explains Adobe's unscrupulous motivation:
As a valued long-term customer, we are pleased to offer you the latest Photoshop CC subscription at a discounted price of $13.79 per month, along with an additional eight free months on an annual plan, as approved by our management team (one-time exception). This discounted price offer is available only for limited time period. The latest Photoshop CC subscription includes the following benefits:
Bunch of thieves, in my opinion.
Thomas