Coastline

Where does the coastline data for those maps come from? Maybe it would be better to redraw them using a more deatailed source, such as Natural Earth (https://www.naturalearthdata.com/), Vector Map (https://gis-lab.info/qa/vmap0-eng.html) or World Vector Shorelines (https://www.ngdc.noaa.gov/mgg/shorelines/, https://data.humdata.org/dataset/global-lsib-polygons-detailed?) (simplified, if needed, in order to reduce file size)?

Also, I tried to make my own world map based on OpenStreetMap data with coordinates rounded to 0.1 decimal degrees. It is small enough for web apps (around 3 MB) and precise enough for a printed A0 wall world map (scale around 1:30000000), but at higher zoom levels lines appear a little blocky, so I'm not sure if it's good enough.

[aourednik]

I know the coastlines ar off in many places. I correct relevant places as I go, based on OSM.
The coastline for 123000 years ago is based on palontological materials about Eurasia. Other continents need work.
The Aral sea "hole" in the Eurasian topology represents its actual extent until 1960.
I don't have resources redraw the coastlines of over fifty world maps (manual work would mean hundreds of hours). I've tried with the "snap geometries to layer" algorithm provided by QGIS, using a more precise world landmass as reference, but the result created more problems than it solved.
If you can write an algorithm that would snap all coastline points - and only the coastline points - to the landmass reference, that would be of great help