Bluetooth lagging on Macbook Pro 16 inch 2019
Interference in the 2.4 GHz range is very hard to measure and even harder to control.
Look to eliminate every single USB-C connection within 10 feet of either device to ensure you’re not generating the interference right next to the Bluetooth receiver on the Mac.

https://support.apple.com/en-us/HT201163
https://support.apple.com/en-us/HT201542

If your display connects via Thinderbolt 3 or USB-C this testing is not ideal but necessary. I have had one person add a USB Bluetooth low energy dongle at the end of a 6 foot (2m) type cable and tape / attach it to the wall next to where they sit so they escape interference close to the Mac. Most of the time, we use another radio frequency if the interference is coming from too close to eliminate.
Also, all sorts of electronics and motors can cause the interference, check everything in 30 foot range if you can’t get an actual tool to measure the RFI.