@reinhard,

Now that Designer is "DPI aware" you can change the Windows Display Scale factor (in Settings | System | Display) to any value that you like. The program will scale it's UI elements up and your drawings will still be at the full resolution of the monitor. (All "DPI Aware" apps will do the same.)

Try 125% first and see if that works for you. If not try 150% and larger values. You can change it while Designer is running to see the changes immediately.

Phil