HI Ferry,
The basemaps used by geographic axes are in a Web Mercator (WGS84) map projection. Your data are in the Amersfoort/RD projected coordinate refernece system. You can place your coordinate data into a geographic point shape object and set the GeographicCRS object and then use geoplot. Here is the modified code that plots the point as intended. You can see the difference below. geoplot(lat,lon) assumes the latitude/longitude values are in WGS84. The point in red is in the corrected location.
name = 'openstreetmap';
url = 'a.tile.openstreetmap.org';
copyright = char(uint8(169));
attribution = copyright + "OpenStreetMap contributors";
addCustomBasemap(name,url,'Attribution',attribution);
x = 155000;
y = 463000;
p = projcrs(28992);
[lat,lon]=projinv(p,x,y);
shape = geopointshape(lat,lon);
shape.GeographicCRS = p.GeographicCRS;
figure
geobasemap openstreetmap
geoplot(lat,lon,"Marker","o","MarkerSize",25,"MarkerFaceColor","blue","Color","blue")
gx = gca;
gx.InnerPosition = gx.OuterPosition;
gx.ZoomLevel = 17;
hold on
geoplot(shape,"Marker","o","MarkerSize",25,"MarkerFaceColor","red")
