Significant internet dip when launching BF6

Patryk2k1​ There are a number of things that could be at play here

CPU saturation from decompression/processing: Battlefield downloads and streams compressed assets. If your CPU is busy decompressing or handling game threads, it can starve the networking stack. Speedtest then reports artificially low speeds because the CPU can’t keep up with packet handling.

Turbo Boost / PBO instability: enabling Turbo Boost or Precision Boost Overdrive can cause voltage/frequency oscillations. That instability can slow down decompression threads and even affect NIC (network interface card) driver scheduling, making Speedtest results nosedive.

I noticed in the screenshot you posted to  OskooI_007​  that Turbo was enabled. That could be a potential factor and would be worth turning off in the bios and testing speeds again. 

Network stack contention:  Battlefield 6 may open multiple connections for telemetry, matchmaking, or background updates. These can interfere with Speedtest’s sockets, reducing available bandwidth for the test. 

I think we can eliminate Network stack contention as Speedtest.net's sockets require TCP port 8080 to be open for outbound connections to function correctly. To my knowledge BF6 does not utilize TCP port 8080

Disk I/O bottleneck: Speedtest writes temporary data to disk. If Battlefield is simultaneously streaming assets to your SSD/HDD, disk contention can slow Speedtest’s ability to measure throughput.

Update 

My own testing as follows

From bottom to top speed tests ran in the following order: No BF6, BF6 Splash Screen, Loading Shaders/menu and Conquest Match

There is around a 90% drop in DL  and 54% in upload speeds from No BF6 to in game