Yes and no. Half of the screen was refreshing at a time, so it was really flashing at 30Hz. You still had a visible stroboscopic effect. True 60Hz and 100Hz screen appeared in the late 90s and made a visible difference in term of comfort of viewing.

I think you're mixing monitors and TVs together.

CRT TVs only supported vertical refresh rates of 50Hz or 60Hz, which matched the regional mains frequency. They used interlacing and technically only showed half the frame at a time, but thanks to phosphor decay this added a feeling of fluidity to the image. If you were able to see it strobe, you must have had an impressive sight. And even if they supported higher refresh rates, it wouldn't matter, as the source of the signal would only ever be 50/60Hz.

CRT monitors used in PCs, on the other hand, supported a variety of refresh rates. Only monitors for specific applications used interlacing, customer grade ones didn't, which means you could see a strobing effect here if you ran it at a low frequency. But even the most analog monitors from the 80s supported atleast 640x480 at 60Hz, some programs such as the original DOOM were even able to squeeze 70Hz out of them by running at a different resolution while matching the horizontal refresh rate.

I'm guessing you're talking about interlacing?

I've never really experienced it because I've always watched PAL which doesn't have that.

But I would have thought it would be perceived as flashing at 60 Hz with a darker image?

Yeah I remember I could not use a CRT computer monitor at 60Hz or less for any length of time, as the strobing gave me a headache.