Alfredo Jahn wrote:
So using Parallels? I can install HS in a VM and it will work on a new Mac (2020)? I assume the new ones come with Catalena or Big Sur preinstalled?
When you consider the cost of purchasing Parallels, and the extra work of installing the older OS there plus the performance hit for running your normal MacOS plus the virtual machine MacOS (which will take considerable extra disk space and memory), you are probably better off replacing your Photoshop CS3. Adobe has ceased all support for Photoshop CS3:
"In July 2017, activation servers for CS3 applications were shut down. Registered users who wished to continue using Photoshop CS3 after that date could use their valid serial number to download a new installer from Adobe that could be activated without contacting a server. In December 2019, Adobe stopped providing CS3 downloads entirely." https://adobe.fandom.com/wiki/Adobe_Photoshop_CS3
At some point you will find it impossible to install or continue to run Photoshop CS3. You will need to do a new install into that VM if you go that route. It might be time to consider switching to the annual fee version (Adobe CC) or some other alternative program, such as those mentioned by dialabrain earlier.