The purpose of Escape from Tarkov’s technical alpha starting on August 4th is to see how the game works under strain. It is not to provide everything that will be in the game for evaluation purposes, nor is it trying to display all of the polish that the game will have on release. Invitations for the alpha will be distributed in waves, with all purchasers eligible for this wave of alpha testing scheduled to receive access within two weeks of the test beginning.
It’s also important to note that the game’s servers will not always be available, as this is a testing environment and bugs and stability issues will need to be addressed. Players who purchase a package with pre-order access after the start of the testing will be added into the subsequent wave of testing invitations rather than getting right into the game. For more details, check out the official rundown.