My bug report has been ignored for a month, so I'll post it here then, as it's same issue.

Put in 3840x2160 resolution, nothing fits:

i get the feeling they rarely check these.

I have the same issue as well at (2560x1440) and OnBoard's screenshots show it quite well.

If I drop down to 1920x1080, the UI scales correctly and everything stays on screen.

Also please note in OnBoard's 3rd screenshot how the XP bar obscures the "My Heroes/My Deck" button at these high resolutions.

The only workaround I've found to compare items is to disable inventory auto sort and put the item I want to compare against equipped in a bottom left bag slot. There is no workaround for comparing shop items however.

patch 23 aug ,

not fixed , for me @ 2560*1440  it got even worse

While the OP's issue appears fixed on my end this was mostly fixed by placing the shop items on the left side of the screen so that there is enough room on the right to hold the comparison.

However the varied issues reported in the comments are still present:

1. Ascension XP bar overlap with My Heroes/My Deck
• I've logged this one separately in case that's Trendy's preference since there are numerous other UI scaling issues at high resolutions reported here.
2. Comparing equipped items in inventory
• The problem for this one only changed position. It used to cut off the top of the comparison. Now since they are aligned to display down from the source item location (as of 1.1), they cut off the bottom.