my fotos from Canon powershot G7x markIII are two hours wrong allthough the time is marked right

Select all photos together in Photos, that need the timezone to be corrected.

Then go to the menu "Image" and click "Adjust Date & Time".

See: Add titles, captions and more to photos in Photos on Mac – Apple Support (UK)

"Change a photo’s date and time

1. In the Photos app  on your Mac, select the photos you want to change. Command-click to select more than one photo.
2. Choose Image > Adjust Date and Time.
3. Tip: You can also double-click the date that appears in the Info window to change the date. To show a photo’s Info window, double-click the photo, then click the Info button  in the toolbar. 
4. Enter the date and time you want in the Adjusted field.
5. Click a time zone on the map and choose the closest town/city, if necessary.
6. Click Adjust."

There is one hitch: When you select a different timezone and a different closest city, Photos will just convert the current date&time to a different timezone. The photos will be still sorted as they are. To ensure, that the date and time will be adjusted to the correct timezone, copy the date and time from the field "Original" to the field "Adjusted". Both field should be showing the same time, if you just want to correct the timezone, but not the time.

You can edit the time zone in Photos via its change date panel. The time zone display I mentioned in my previous post helps with this.

Obviously the time zone is then incorrect.

Photos info time zone display can be enabled via the Terminal with (re-launch Photos so it takes effect):

defaults write NSGlobalDomain AppleICUTimeFormatStrings -dict-add "2" "HH:mm:ss z"

...and reverted to the default time zone-less display with:

defaults delete NSGlobalDomain AppleICUTimeFormatStrings

You're welcome 😊 Graet that it worked for you. Matti had the right idea about the timezones.