What is a single thread?

Dart/Flutter is single threaded and not possible to share global variable. As each isolate has its own memory, space and everything. To make it work like multi-threaded you have to use isolates and the communication will be used through ports by sending message to one another.

single thread in British English noun. computing. the execution of an entire task from beginning to end without interruption .

Generally speaking gaming is single thread intensive on the CPU side , and all parallel task are offloaded to the GPU. This is really more of a workstation or server cpu than a gaming cpu.