Cloning my older iMac to an external drive

[chscag]

My reply was for member "krs" not "DominikHoffmann".

 

[twizzard]

I just went through this exact case myself. You can use Carbon Copy Cloner (which I used) or Super Duper to clone your El Cap computer to an external hard drive. Then you boot your Catalina system in Catalina with the disk attached. Then you can copy your data (NOT programs) to the new computer. You can look at the programs on the clone (in Applications) and see if you can install those programs from the App Store or the web. Do NOT try to copy the old applications to the new computer (there might be a few 64 bit programs that would work, but it is far safer to just get fresh copies). The other thing that really helped was using Lastpass to store logins, passwords, and information on installed programs like serial numbers and installation codes. Lastpass will work perfectly on both El Cap and Catalina, is free and is very secure.