UI lags or seems sluggish even on fast multi-core CPUs in 3ds Max

Issue:

When clicking on various UI elements, 3ds Max windows seem to lag or appear sluggish, even on fast CPUs, such as the Intel i9 or AMD Ryzen Threadripper-series processors.

Causes:

Includes, but is not limited to:

Under certain PC hardware configurations, the multi-core CPU’s cache memory access may become bottle-necked when performing certain calculations. The CPUs may run very fast as long as they can hit the data they need directly (in the cache), but can become stalled when hitting a “cache miss.”
Outdated video card drivers.
Power management options in Windows may be switching between a slower, low-power onboard graphics processing unit (GPU) and a higher-performance video card.
Large 3ds Max scene files (more than 1 gigabyte) with many objects and high-resolution textures can bog down viewport performance.
High monitor resolutions.

Solution:

The following is the most up to date collection of available solutions. It may require one, or a combination of the steps below to resolve:

Disable Hyperthreading (for Intel CPUs) or Simultaneous Multithreading (SMT, for AMD CPUs)

Although it may seem contradictory, disabling Hyperthreading (for Intel CPUs) or SMT (simultaneous multithreading, for AMD CPUs) may actually speed up 3ds Max performance. (Note: the Arnold renderer does take advantage of both Hyperthreading and SMT, so disable these settings only if getting the best performance from Arnold isn’t necessary.)

For Intel CPUs, the instructions at this PC Mag link may be helpful. Consulting the tech support personnel of the PC manufacturer (or of the motherboard manufacturer) may help as well.
For AMD CPUs, please consult the AMD website or your motherboard manufacturer’s website on how to turn off SMT in the PC BIOS or UEFI settings. In addition, the instructions at this link regarding Windows power options for Ryzen CPUs may be helpful as well (although this page recommends not disabling SMT for gaming).

Set a Qt Environment variable in Windows

Some 3ds Max users may see UI improvements by setting a Qt (UI) environment variable in Windows:

In Windows (8 or 10), go to the Search bar, then type in System. (It should bring up the choice of “System (Control Panel).” Press Enter.
In the System menu, click on the Advanced Systems Settings item on the bottom-left of the menu. A System Properties menu will appear.
At the bottom of this menu, click on the Environment Variables button. The Environment Variables menu will appear.
At the bottom of the menu, under System variables, click on the New button to bring up the New System Variable menu.
Variable name, enter: QT_OPENGL = angle
Variable value, enter any one of these:

QT_ANGLE_PLATFORM = warp
QT_ANGLE_PLATFORM = d3d9
QT_ANGLE_PLATFORM = d3d11

7. Click on OK in each menu to save the changes, then reboot the PC and re-test 3ds Max.

Note: if one of the preceding settings doesn’t seem to work, repeat these steps, but delete the earlier variable and replace it with the next one in the list.

Update Graphics Drivers

Instead of relying on Windows Updates or other update version software, periodically go to the GPU manufacturer’s website, search for the latest drivers available for the PC or laptop, then download and install them.

Configure the PC or laptop to use high-performance graphics

See the following articles:

Optimize 3ds Max scenes

Follow the steps in this article: How to optimize performance in very large 3ds Max scenes

4K and above

Drop the resolution to 1080p.