Using DDrawCompat from narzoul has fixed all current issues with these game for me:
- Anno 1602 no longer crashes or causes visual errors when minimizing
- Anno 1503 no longer gets stuck on the loading bar

You can find it here:
https://github.com/narzoul/DDrawCompat/releases
(Click the "assets" tab to access the files, I used version v0.6.0 on Windows 10)

To install just move the "ddraw.dll" file from "DDrawCompat-v0.6.0.zip" into your game folders.
(The same folder that has "1602.exe" or "1503Startup.exe")

it worked firs try, thx a lot!

But it doesn't fit my whole screen if i use the fix. Without the fix the game Anno 1602 did crash once when the music was strangely repeating itself. But am on windows 11
Plus i don't minimize the game when playing

Not sure this will fix your issue but you can try:
- Create a text file in the game folder called "DDrawCompatOverlay-1602.ini" (without the quotes)
- Edit it with notepad and paste in "FullscreenMode = exclusive" (without the quotes)
- Save the file and start the game, once it starts press shift+F11
- Scroll down and check FullscreenMode says exclusive

It says borderless and is there anything i can read about this so i would try to fit the whole screen. I tried your solution but it still says borderless.
Maybe because it doesn't find the file even though i named it .ini without the qoutes like you said and in the game folder i found ddraw compat which mentioned that it didn't find the file. In game i can use shift and f11

Used notepad to try to create the ini file. Well guess i am gonna try it again tommorow

Strange, here is more information about configuration files:
https://github.com/narzoul/DDrawCompat/wiki/Configuration

Just to clarify but are you wanting to get a fullscreen image with a 4:3 aspect ratio or are you wanting it stretched to cover the whole screen?

I don't know it fitted my whole screen with a setting 60hz 1920x1080 on my monitor and it didn't look streched now with ddraw it doesn't fit the whole screen.
I have found out how to make a ini file properly on win 11 but trying exclusive doesn't work as the game just crashes.
My monitor is tuf gaming vg24vq1b asus 24 inch

On a nvidia rtx 4060

Hmm the only other thing I could think of changing would be the "SoftwareDevice" setting.
If that doesn't work I would suggest creating a thread in the support section: https://github.com/narzoul/DDrawCompat/issues