With the preset app to open the photos in Win10 I'm more than dissatisfied. Does anyone know good, free alternatives?

After Win 10 flattened my "beloved" photo ad everything is going on about this stupid app. How nice it was under Win7. Restore? Does not work, because I did not upgrade but have a new notebook.

Open the start menu. Enter regedit here and right-click on it. Select "Run as administrator" and enter your administrator details if necessary. Usually, these are the same as your login credentials for the computer. Select "Yes" when a short warning message appears.

In the Registry menu, follow the path "HKEY_LOCAL_MACHINE" → "SOFTWARE" → "Microsoft" → "Windows Photo Viewer" → "Capabilities" → "FileAssociations".

Now click with the right mouse button on the empty area. Then under "New" select the sub-item "String".

Enter .jpg here.

Right-click on your newly created file. Then select "Change…".

Write in the input field at Value PhotoViewer.FileAssoc.Tiff. Then click on "OK".

Repeat steps 3-6. Instead of .jpg enter the names .png, .jpeg, .gif and .bmp. Keep the value PhotoViewer.FileAssoc.Tiff.

Now close the registry and open any image on your computer. You'll see an ad that says "Windows Photo Viewer." Then tick the box next to "Always use this app to open [Image Format] files" and click "OK." You will need to complete this last step once for each image format. After that, Windows Photo Display will automatically be set as the default program for these formats.

Sounds pretty complicated. I'm not really dreaming about it, I'm scared of "destroying" something, so that nothing will work anymore

Look at picture viewing programs or image management software.

Spontaneously I think of the following:
FastStone, IrfanView, Picasa, XnView

I myself use FastStone as an image viewer, but I have never tried to import the images, so I do not know how good or bad it is. I'm doing the import of images with Windows 10.

You can easily delete the new entries in the registry afterwards, which should restore the initial state. If you are still unsure, you can backup the entire registry beforehand and restore the old backup in an emergency.

From the Start menu, type regedit.exe in the search box, and then press ENTER. If prompted for an administrator password or confirmation, enter the password or confirm.
In Registry Editor, click the registry key or subkey that you want to back up.
Click File> Export.
In the Export Registry File dialog box, select the location where you want to save the backup copy. Then enter a name for the backup file in the File name field.
Click on "Save".

Windows 10 Standard "Program" Setting:

In the Windows 10 Start menu on the far left click on the cogwheel icon (Settings), the window for the Windows settings opens.

At the top of the search bar, type in the word "standard", "stan" will be enough to show below in the Default Apps preferences.

Click on "Standard Apps" to display the window for setting "Default Apps".

See "Picture Viewer" (click) to see if the beloved photo viewer application is available in the App Chooser.

If not, reinstalling the beloved photo display program can help, or alternatively, e.g. Also:

xnview (freeware)

https://www.xnview.com/de/

irfan view (freeware)

https://www.irfanview.de/