I play on a relatively old Mac, the base game runs fine but with the mod pack it doesn't work anymore. Is that normal?
- graphics of resources and buildings are weird
- cutting trees or demolishing buildings lags the game tremendously
End yeah, the fast mod pack is the same

It is possibly a cpu, ram or vram issue. If you are playing in single player you can try deleting the shinybob folder from inside the modpack and see if that helps if it is a vram/ram.

My guess is CPU though. The pack adds quite a bit of scripted mods.