It’s easy to see that sea level rise has not been steady. It has accelerated.
In fact it has accelerated a lot, especially recently. For most of the 20th century, it rose sometimes faster, sometimes slower, but for the last few decades its rise has picked up speed. The clearest demonstration is the change in global mean sea level. There are several different estimates of that based on historical data from tide gauges around the world, which differ on how much and how fast sea level has risen, but they all show — without a doubt — that the rise has not been steady.