I know I was still using 5¼" floppies at least a bit into the early '90s, though it’s been long enough that exact years elude me.
I was also still developing technology that used 3½" diskettes well into the first decade of the new millennium - though I finally managed to migrate newer systems to CD-R around the end of that decade.
I mean 1989 was the last time I used a 5.25 in elementary before everything was switched to 3.5 with the IBM Model 30.
I know I was still using 5¼" floppies at least a bit into the early '90s, though it’s been long enough that exact years elude me.
I was also still developing technology that used 3½" diskettes well into the first decade of the new millennium - though I finally managed to migrate newer systems to CD-R around the end of that decade.