Stumbled upon this in 2023, looks like they have removed gridLines, zeroLineColor and borderColor in v4 (I am on ^4.3.3). Now, we have a separate border configuration in options.scales[scaleId].border as specified here.
options: {
scales: {
x: {
ticks: {
color: '#fff', // Color of the x-axis labels
},
grid: {
color: '#ffffff44', // Color of the x-axis grid lines
},
border: {
width: 2,
color: '#fff', // <-------------- Color of the x-axis
},
},
},
},