Hard to say from the photo. The one on the right is certainly much brighter.

I have a similar setup - my left monitor is a Dell Ultrasharp and my right monitor is a BenQ ZowieXL.

The BenQ is RIDICULOUSLY bright out of the box and I had to drastically reduce the brightness in order to use it for regular day to day computing. The game presets look amazing while running a game but are terrible for looking at literally anything else, and even the standard setting is blindingly bright by default.

I did some tweaking and they still aren't quite the same, but it's fine for me. They're close enough.

That works about 95% of the time, but not even that's guaranteed. They really need to be out of the same batch. We've had noticeably different colour rendering on the same monitors but different production months.

Unfortunately this is the reason you should always have the exact same monitors for dual monitor setup, without calibration the image may be completely different, especially in cheaper monitor where the color delta may be up to 10-15 (up to 1.5 is considered professional grade accuracy and up to 3 is considered very good for non-professional use, over 5 is considered off). Some monitors are warmer and have vanilla white instead of fresh chalk white, some monitors have different gammuts, contrasts, brightness, colors, input lags... so many things can be different that the overall experience is "annoying", because the bad attributes are amplyfied if have comparison right next to it.

So you can try to play with different setting but I am afraid that you wont be able to fix more than 50% of the overall difference, choose which monitor you like better, get another one and sell the worse one.

One is TN and the other is IPS probably.

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Edit. Well i checked models. Both are TN. IDK. maybe peak brightness in the monitor itself?

I'm more or less trying to figure out what to look for in a monitor. Neither one has HDR, but the left one clearly displays deeper colors.

To get them looking alike, you’ll need a calibration device and the accompanying software.