If your current video drivers are up to date, either Trace Reference is on or you might have a "Material Priority Problem" if you migrated the project from an earlier version of AC.
AC18 is not slow on my side.
eduardo rolón AIA NCARB
Another of the forum moderators.
Macbook Pro M1 Max 64GB ram
OS X 10.XX latest
AC25 US/INT -> AC08