I know it's still seeing some use, but the steady reduction in use was very noticeable already during my school years in the 80's and 90's, and appears to have continued. Some use will still certainly persist for a long time.
The fun thing is we can easily quantify the relative rise and decline in written use at least by searching the national library (nb.no) for newspapers. I've only done the search for one set of numbers, so a major caveat that maybe there's large variance between different numbers, but a search for "fem og tredve" combined with "femogtredve"
* 2000-2024: 412 newspaper hits
* 1950-1999: 3112 (caution, different bucket sizes)
* 1900-1949: 4303 (before the reform)
(the "halfway point" og "fem og tretti" is also in use; 42 between 2000-2024, but never very widespread)
vs. "trettifem":
* 2000-2024: 2587
* 1950-1999: 5728
* 1900-1949: 69 (before the reform)
(You can break down the search results in finer chunks too, but I think this gives enough of an indication)
But the difference in common use has steadily diminished. When I grew up in the 1970s and 1980s many of the most conservative forms of Bokmål were already falling out of favour, and my teachers were constantly pushing for us to use the forms matching our dialects, which for most people (I grew up near Oslo) meant a greater overlap with Nynorsk even then.
So while "Samnorsk" isn't being talked about much any more, in practice the gap is steadily diminishing.
What I think is quite remarkable is that this gradual merging has seen Bokmål, partially due to politics, change at least as much as Nynorsk. (For two languages so close together, language has been extremely political in Norway, though "peak language politics" was probably reached in the 1970s.)
Many "Danishisms" like "reverse numerals" ("fem og tredve" - "five and thirty" - instead of "trettifem" - "thirty five") that were widespread still in my childhood are now firmly old-fashioned, for example.