Bootcamp Bluetooth mouse lagging when WiFi is enabled
UPDATE #2 (27/0/2020)
Driver's Version 7.77.119.0 [21/4/2020], also works nicely with Antenna Diversity -&gt; Aux and Bluetooth Collaboration -&gt; Auto.

UPDATE #1 (12/1/2020)
I can confirm that the newer version of the driver (7.77.110.0 [10/10/2019]) also works smoothly without any configuration.

After all, I found the solution here.
I disable the Bluetooth Collaboration option and I change the Antena Diversity property to AUX.
Instructutions:

From Device Mananager (Windox key + X)
Select Network Adapters
Double click your adapter (mine is Broadcom 802.11ac Network
Adapter)
Click Advanced tab
For the property Bluetooth Collaboration select value NO
For the property Antena Diversity select value AUX

Instantly my bluetooth mouse worked smooth alongside my WiFi adapter.

If you don't see the two above properties you may need to downgrade your network's adapter driver.
As I saw those properties are available for:

Broadcom 802.11ac Network Adapter Version 7.35.118.40[7/24/2015]
Broadcom 802.11ac Network Adapter Version 7.35.118.73[7/12/2017]

But NOT in the latest version:

Broadcom 802.11ac Network Adapter Version 7.35.118.83[4/20/2018]

More info here.