I am surprised to see that there are very few relevant standard preview size settings for people using a 4k monitor. The maximum setting is 2880px and then "Auto". Lightroom is choosing 6720px on the "Auto" setting which is massive and (I presume) contributing to Lightroom running extremely slow. This is all while running a brand new 16" Macbook Pro with 32gb of RAM, AMD Radeon Pro 5500M 8 GB, and 2.3 GHz 8-core i9 processor.
Please include more preview size setting in between 2880px and 6720px for people working on 4k monitors.