I also used this nirsoft Software, called out by Morphy81 earlier.
I could not find my ".tif" extension in the Apps>Default Apps (for whatever reason).
Luckily, this nirsoft FileTypesMan still registered ".tif" https://www.nirsoft.net/utils/file_types_manager.html Editing all the properties of the ".tif" according to any other image file extension ("e.g. .tiff") in the nirsoft FileTypesMan
worked. After a restart, the .tif extension was found again in the Apps>Default Apps. I can now just edit it the "normal way" -great.
Unfortunately, I found a worrying post on the Nirsoft software (https://www.borncity.com/blog/2020/04/14/die-nirsoft-tools-und-die-dll-hijacking-schwachstellen/). I don't intend to diminish the work by Nirsoft, since it worked as a charm for me, but:
using third party software to solve a problem related with something essential as file-extensions in Windows - that was not solved by the Windows support team! - is always some sort of security issue, that I really hope to avoid.