Docs for v8.0 state the following here

storage.wiredTiger.engineConfig.cacheSizePct

Type: float

Defines the maximum amount of memory to allocate for cache as a percentage of physical RAM. The memory that an index build consumes (see maxIndexBuildMemoryUsageMegabytes) is separate from the WiredTiger cache memory.

But v8.2 release notes state this here

WiredTiger Cache Size Configuration as a Percentage

Starting in MongoDB 8.2, you can configure the WiredTiger internal cache size using a new percentage-based option. In addition to the existing --wiredTigerCacheSizeGB and storage.wiredTiger.engineConfig.cacheSizeGB gigabyte-based settings, you can now specify the cache size as a percentage of the available memory with the --wiredTigerCacheSizePct and storage.wiredTiger.engineConfig.cacheSizePct options.

I think this is a bug on the documentation misleading people to believe that v8.0 has such feature available?