Using the Android App there isn't a way to run a speed test. 

Just purchased and received TP-Link Deco AXE5400 Tri-Band WiFi 6E Mesh System (Deco XE75 Pro) - 2.5G WAN/LAN Port  2-Pack from Amazon via https://www.amazon.com/dp/B0B89L8QKZ?ref=ppx_yo2ov_dt_b_product_details&th=1.

I am connected to a Motorola MB8611 DOCSIS 3.1 Multi-Gig Cable Modem Approved for Comcast Xfinity  2.5 Gbps Port and it has 2500 Mbps Max Internet Speeds seen via https://www.amazon.com/dp/B08DDFKXKC?psc=1&ref=ppx_yo2ov_dt_b_product_details 

Need to prove that Xfinity / Comcast isn't delivering an acceptable speed and there isn't a speed test on the app.  Plugging into the equipment with my cable and laptop isn't an answer as I will want to run speed this test often and it isn't convenient to stand/sit with a laptop. Defeats the whole purpose of WiFi.

This is unacceptable.   

Has TP Link made deals with providers like XFinity, Spectrum, Cox, etc.. so that they can get away with delivering poor speeds?

This is a Bug this is not a Feature Request.  As so many of your ohter apps has speed tests included.