The physical Tretyakov Gallery is, of course, closed, but it has a wealth of online excursions and films, and is starting a series of concerts, films, excursions and lectures with the hashtag #ТретьяковкаДома, which can be found here. Most are in Russian, but upcoming concerts held in the halls of the museum don’t require any language ability - just a desire to hear beautiful music surrounded by magnificent art.
If your Russian isn't strong, you can still spend a delightful evening on the English part of the gallery site, where there are also some short English-language videos.
But the real treasure trove is the Gallery’s YouTube channel where there are dozens if not hundreds of films, lectures, and curated walks through permanent and temporary exhibitions. These are almost all in Russian, but there are Russian subtitles to help you.
There are also a few films in English, some made by the Tretyakov Gallery, some by other organizations or individuals. They can be found here.