Something low-resource demand (like my blog) would probably be okay, save for a few large pics on some pages. Most people who run in the smolweb circles also like vintage computing, so creating webspaces using only HTML & CSS is common practice, which should do fine over a 56k connection.
No need to wonder, just end up in an old building with thick brick walls that are only penetrated by a weak 2G signal and try to load something on your phone.
Not possible anymore is many areas, where 2G and 3G networks have been shutdown to re-use spectrum for newer standards. The last time I was in a rural area with minimal signal strength, my phone was alternating between satellite-only messaging or 5G with 5-10 MB/s. I was actually able to download a movie in a quite reasonable amount of time, presumably because there wasn't anyone else doing much with the cell tower I was barely in range of.
Out in rural Michigan, there are plenty of spots where an LTE signal technically exists but you can't do much beyond calls and texts (and even those fail sometimes), and it's interesting to see what apps still work. For instance, YouTube will still load and play videos, albeit at an abysmal pace that's really not worth it (and it's interesting to see how the app prioritizes the video itself over its metadata, to the point that you could watch an entire video in 144p before the channel name and description load), while my bank's app just fails entirely despite ostensibly requiring less bandwidth than video playback.
You can test it yourself in the comfort of your gigabit connection. I wanted to test my barrage of very small images using lazy loading on a crappy connection. I learned that Chrome can easily pretend to suck. On Safari you somehow need to download a special tool but it works just as well.