If you wish to explore actual data sets ... then here you go ...

The independent European ones ... https://cds.climate.copernicus.eu/datasets

The Independent Berkeley data sets ... https://berkeleyearth.org/data/#:~:text=Berkeley%20Earth%20provides%20high%2Dresolution,areas%20reported%20back%20to%201750.

and of course the NASA datasets ... https://www.nccs.nasa.gov/services/climate-data-services

Regarding the questions you ask, they are good questions, why is it not a linear line. It is basically because the climate system and the energy imbalance is not linear, but instead is a deeply complex system.

You can also step back and ask yourself this - If the world really is on average warming, then more heat in the oceans will lead to water to expand and more melting of ice both together with lead to a rise in sea level, so has sea level been rising since the onset of industrialisation?

Yes, it has, its really really has - https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level