On Mac you will need Snow Leopard (or older) to open the oldest converter programs (Snow Leopard comes with Rosetta emulator for PowerPC programs). That means you will need an older Mac too, unfortunately.
A win-PC could be of help with those older converters.
ps. I can't let my iMac 2007 go because of this compatibility reason. Sometimes we are asked to dig out some 15-18 year old files.
AC25, Rhino6/7+Grasshopper, TwinMotion • Mac Pro 6,1 E5-1650v2-3,5GHz/128GB/eGPU:6800XT/11.6.5 • HP Z4/Xeon W-2195/256GB/RX6800XT/W10ProWS