External Monitor Blurry text and Sluggy Mouse on MBP 2020

Solution 1:

The issue that you’re having is that you driving a massive monitor on what amounts to an “entry level” MacBook Pro. That particular 13” MacBook Pro doesn’t have a discrete GPU so it has to share all of the graphics processing with the CPU. Additionally, it’s using up to 1.5GB of your system RAM as video memory. You can see this when you disconnect the external monitor, the mouse no longer lags; it’s because the CPU isn’t working hard to drive that monitor.

The reality here you’d most likely do better with a higher end MacBook Air than you would a low end MacBook Pro. (IMO) the reason you get a “Pro” is for the discrete video and higher memory capacity. If you’re not getting the Pro with the AMD Radeon GPU and the maximum memory, you’re not getting full value.

If you are within the return window, I’d return it and either get a MacBook Pro with a GPU (even a used one) or get a higher spec MacBook Air and save some money.

Lagging mouse

You shouldn’t need native Logitech drivers to make your mouse not lag. If you don’t have them, your Mac will use the standard USB HID device drivers from Apple and it will behave like a generic 3 or 5 button mouse. The additional software from Logitech is merely for all the special customizations that Logitech brings to the table. The fact that the mouse performance returns to normal when you remove the external display confirms that it’s not a mouse driver issue.

Cables & Connections

Your HDMI cable isn’t going to make things better in terms of blur or color or mouse lagginess. The signal(s) that go over these cables are digital (1s and 0s) meaning you can introduce a ton of noise on the cable and it will still be a digital signal at the end. Cables quality matters in terms of build quality (how it flexes, how the ends were molded, if the pins are not shorted, etc.) I recommend high quality cables to protect your equipment and ensure a reliable connection, not to fix display quality issues because, if it didn’t have the required bandwidth (met the HDMI spec in question) you wouldn’t get the resolution and frame rate that you’re getting. Blurriness is a factor of the wrong resolution for your particular monitor.

You should use a quality DisplayPort cable instead of converting to HDMI. If you notice, your “Connection Type” is Thunderbolt/DisplayPort (last line of your system report), but you’re using HDMI. This means you’re converting from the native DisplayPort signal to HDMI; this can introduce video issues. I’m a staunch proponent of not converting signals and sticking to DisplayPort. You Dell monitor supports DisplayPort so I would go with that first and if you must go HDMI, use an active adapter.

TL;DR - Possible Fixes

Connect monitor via DisplayPort and not HDMI. Not having to convert a signal is inherently more efficient and more reliable. The Dell P2719H accepts DisplayPort as an input.
If possible, get a MacBook Pro with a discrete GPU (if within the return window). The 2020 13” MacBook Pro with 1.7GHz CPU uses the 8th Gen. Intel Core processor where as the 2020 MacBook Air uses the 10th gen. The latter being more efficient for less money.
Downscale your monitor to no larger than 22” FHD display. You’re driving two displays, one of them a massive 27” with nothing but integrated graphics. The less your CPU has to render, the more efficient it will be.

Solution 2:

How is your HDMI cable connected to your USB-C on the MBP side? I had similar issues and realised that certain combinations of HDMI or HP Display port cables in conjunction with cheap Ali-express converters to USB-C resulted in either a blurred external monitor or even sometimes in the MBP monitor being blurred and the external monitor being perfectly clear.

So if you have the chance, try using different cable combos, just to see if it makes a difference.