+ and - icons of the directories are too small

The icons that represent the directories are very small even though I changed the scale of my windows to 160%
or changing the DPI settings of "dopus.exe" doesn't work.

The size can't be changed.

Yes, I understand
however there should be a change in these icons in a future version.

For someone who wears glasses like me, they are too small.

The size comes from the Windows visual style.

Change the folder tree to use the default visual style again and you'll get slightly larger arrows instead of the + and - boxes, but beyond that the size of them is defined by Windows and your system DPI.

You'll see exactly the same size tree expand/collapse buttons in pretty much all other Windows software, so if they are too small in Opus then they'll likely be too small in everything else as well, and you might want to increase your system DPI scaling a bit more.

(I recommend against overriding the DPI settings on dopus.exe as it probably won't solve anything and may cause problems instead.)

So all the programs are really small but the ones I use the most I have changed the particular DPI of each program.

where is this configuration ?

Change the folder tree to use the default visual style again and you'll get slightly larger arrows instead of the + and - boxes, but beyond that the size of them is defined by Windows and your system DPI.

Instead of overriding the DPI for every program, why not just set the system DPI to something larger? That will make everything larger from a single change.

where is this configuration ?

Preferences / Folder Tree / Appearance. (It must have been changed in the past as it defaults to "Visual Style" which is different to the "Lines" setting you're using.)

Note also that the actual click area is larger than the visible button.