Hi Karl,
Yes, as Eduardo notes, Graphisoft announced over a year ago - perhaps 2 years? (cannot remember without a search) - that 12 would be the last version that would run on PPC (G4/G5) Macs, more or less in synch with Apple having Leopard (10.5) as the last OS that would run on those PPC machines.
The specs do say either Leopard (10.5) or Snow Leopard (10.6) for 13. I don't know if it would run under Tiger (10.4) as I don't have an Intel machine with Tiger installed. I do think that the increased functionality (and speed) from the OS upgrade is tremendous and worth it for anyone with older Intel machines. Besides quick view, Time Machine, and so much more, a feature that saves me tons of time in Leopard is the search box in the Help menu of every application which searches all of that app's menus. As many commands as there are in ArchiCAD, it is sometimes hard to remember where one is - especially on someone else's customized WE ... and typing into the Help box instantly gets you there.
While PPC machines cannot run Snow Leopard or 13 (or 13's BIM Server), a Power Mac G5 with Leopard (for Time Machine backups) could still be a useful file server in the office, and perhaps useful for other tasks.
2 GB minimum systems memory for Mac or PC; 4 GB or more recommended.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB