" Another says simply to tighten the drive side (again, incrementally). " PO

I think I would avoid this advice, being the opposite of where you want the rim to go

Second thing I think of- If 1.5 mm of added clearance, on one side, will make the difference I would consider the tires too wide for the frame.

The best no cost way to learn to true wheels is to have no skin in the wheel you start with. Find a low/no cost wheel with lots of spokes and play with it. Front or rear doesn't matter. Just that you have a sample to learn nipple work with rim deflection played off of spoke tension. Wheel truing is a massive shade of grey compared to adjusting a gear system or installing bearings. Absolutes are less important than relativeness is.

Last thing I think of with this post is how well made the OP's wheels were to begin with and how their parts will make learning to true a wheel harder than if started with a far less "performance" intended one. The OP's wheel has few spokes that are rather thin, likely with AL nipples and laced to a fairly stiff rim... Andy