How to search by movie release attribute?

I don't see how you would do that with Advanced Title Search.

https://www.imdb.com/search/title/

Some titles have a trivia item about it:

https://www.imdb.com/search/title-text/?trivia=TIFF

That search is part of the Advanced Searches listed when you change the All dropdown to Advanced (next to the search box atop nearly every IMDb desktop page), or bookmark this: 

https://www.imdb.com/search/

If you want to do some data-mining, the festival attribute looks like it's part of this dataset:

title.releases.tsv.gz - Release dates for the various regions for a title.

• titleId (string) - the tconst, an alphanumeric unique identifier of the title
• ordering (integer) - secondary key to uniquely reference items with the same tconst
• date (string) - represents the release date of a title
• region (string) - the ISO Alpha-2 country code
• premiere (integer) - flag indicating if this was the premiere release
• wide (integer) - flag to indicate if this was a wide release
• premiereType (string) - description of the type of premiere
• festival (string) - indicates if this was a festival release
• attributes (string array) - other attributes or comments

BTW, there's section of IMDb dedicated to TIFF:

https://www.imdb.com/toronto/?ref_=helpms_ih_gi_siteindex