xCode - Can't enter values in Add New Constraints boxes

did you first click on the red dotted line to activate the constraint ?

line :

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Could you detail, may be post a link to a video : If I position subview well off sides then this issue doesn't happen

It seems you are not bthe only one to have similar problem.

https://forums.developer.apple.com/thread/127105

I also encountered this problem, this problem should be macOS10.5.2 caused by this system, I tried to install Xcode11.0 version, still have the problem, but I run this on MacOS10.14.6 Xcode11.0 is no problem, such as apple update system fix the bug, also don't know if you have met the Xcode run for a period of time can cause the CPU occupancy rate reached 100 +, in turn, and fan CPU temperature is high, this is all the macOS10.15.2 system itself, I guess Test. First of all, I can confirm that my computer configuration is ok. The new i9 processor with 16 "32gb memory is the best.

XCode 11.0 is now a bit old and had many issues.

Should update to 11.3 and retest.

On the screenshot, you have defined 3 constraints for Top, leading and trailing.

These are the directions in which you cannot set a value to struts when adding new constraints.

First remove (or deactivate) those (try with top) and check if you can now set a value.

Thanks to feedback and close the thread if appropriate.

I am also having exactly same issue as pddltd is having.. My XCode version is 11.3.1 (11C504) and MacOS version 10.15.3 (19D76). After adding constraints like this, I need to modify their values from size inspector to get the desired result.

Still happening on 12.5.1