EXTERNAL DISPLAY PROBLEM -

specs for that display show multiple connections possible:

Connectivity:

HDMI (v1.4)

DisplayPort (v1.2)

Mini DisplayPort (v1.2)

if you are using HDMI, HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"Premium High Speed HDMI cable" or that + "with Ethernet" --OR--

"Ultra High Speed HDMI cable" or that + "48G"

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

if you hare using [√] Mirror Displays, your Mac computes a compromise resolution that BOTH displays appear to be able to reach. It then refreshes BOTH displays with ONE rasterizer/display-generator, and they will be EXACTLY the same resolution and in Sync.

note there are TWO blue rectangles, but they are nearly superimposed on each other to show they are being Mirrored.

Macs generally consider displays 2K and smaller as "not eligible" for use of "scaled" resolutions, because the improvement Scaled creates is very small at that resolution, or possibly negative.

For my use, I prefer to make some adjustments in individual Apps to get text better matched to my vision:

for larger fonts on web pages, I set Safari to "never show [default] fonts smaller than 16 point". I expect Chrome has similar settings.

for larger fonts for displaying lists of files, there are settings in Finder that can be modified for larger fonts in list view, and larger icons and/or fonts in icon views.

the menubar is bold enough that It has not been a readability problem for me.

If you uncheck that checkbox, you will get an Extended desktop instead:

Now the two displays are shown in their relative "real" resolutions, and are concatenated along any edge of your choosing. The Mouse-pointer moves freely across the invisible boundary between displays, and can carry a window all the way or even part way across the boundary.

Then I do not understand your issue.

I use a 2560 by 1600 display all day every day without any "scaled" settings, and it seems fine for my bad eyes.

¿are you using "scaled" settings? that should make text [only] larger.