Many thanks for your file! This shows the following error:
+ MsiOperation result: 1612
This occurs when the installer cannot find the MSI file for your currently installed version. The usual cause for this is a third party 'cleaning' app, such as CCLeaner, as they tend to remove/clear some of the Affinity folders, including the installer files.
Can you confirm, do you have any such app installed on your computer?
In the meantime, we'll need to manually uninstall the current version, so that you can install the latest update. Please download the below tool from Microsoft -
https://www.dropbox.com/s/h485c2eoqisjrr8/MicrosoftProgram_Install_and_Uninstall.meta.diagcab?dl=0
Once downloaded please run the tool, select Uninstalling and then Affinity Photo from the list of apps shown.
If you can't see Affinity Photo in the list, select the aptly named first option and then paste the following code in and select OK.
Depending on which version you most recently had installed, the code will be slightly different but I believe you'll require the first one below:
{E0A227B9-8299-48C6-9FB2-71140FEF82B4}
{958C8ACD-8C7A-43ED-92D7-B25B263CAFDA}
Once the uninstaller has completed, please visit the following link and download a fresh copy of the latest exe, then navigate to the downloaded .exe right-click on the file and select Run as Administrator, this should hopefully install the app for you as expected. https://store.serif.com/update/windows/photo/1/
I hope this helps!