Blender Viewport Lag
Slow viewport and low frame rate while working
Also known as: Blender slow viewport · Blender laggy · Blender viewport slow subdivision · Blender simplify · Blender performance
Quick answer
A slow Blender viewport usually comes from too many subdivision levels, heavy modifiers, high-resolution textures or an expensive shading mode. Lower the Viewport level of the Subdivision Surface modifier and keep the Render level high, switch to Solid shading while modeling, hide heavy collections, and turn on Simplify in Render Properties to limit subdivision and texture size.
How to fix it
Use the Decimate or Multires modifier carefully, since both can be heavy at high levels, and turn off overlays and statistics you do not need. Work with lower-resolution proxies of big scenes, and check Preferences > System to see that your GPU is used for the viewport. For sculpting, reduce the brush detail or use Voxel Remesh to a manageable polygon count.