Is there any device out there that will purposely slow down my 4g lte / 5g on my phone to test something ?

[ng4ever]

I have a iPhone 11 if that matters on what device I need. Thanks.

 

[Zepher]

Yes, a Rockwell Turbo Encabulator will

 

[SamirD]

If you're talking about the wifi speed, just use a 802.11n access point or put a 10Mb switch or hub in between the access point and Internet source.

 

[Zepher]

Also, the device you are seeking would be illegal to operate.

 

[ng4ever]

True I want it for myself though

 

[Keljian]

A metal box will work

 

[SamirD]

A metal box will work

For cellular signals, this will do the trick. If you want to be cheap, just wrap the phone in aluminum foil.

 

[Nobu]

You could set up a proxy in your apn settings which has a throttled connection, maybe? Only works for some connection types though, I think.

 

[Nicklebon]

Micro cell with an ethernet backend running through wanem.