More computer woes

I'm not getting on at all well with my attempts to use CAD software to generate the data needed for my 3D printer. Not only do all the programs I've managed to try so far have a far from intuitive user interface (or fail to even install!), but some of them either run over the internet, or only store their data via the internet. This means you are totally dependent on the whims of the company regarding their continuing to make the software available (and at what price?), but the service is not to be relied on, and they control all your data. Fusion 360 is very unreliable - you do have the program on the local computer, but some operations take place centrally via the net, and they can be very slow,, or fail completely (like this SLA export, which fails like this quite often).