Assigned male at birth is the term you want to use. “Biological male” is a term used by transphobes to spread misinformation.

Biology is very complex and not your elementary school version of biology. What makes someone “biologically” male? Is it having a penis, having testis, having more testosterone than estrogen, having XY chromosomes? These can all be intermixed with other characteristics.

The “basic biology” definition doesn’t work in the real world, and the people using it are actively trying to harm trans people or ignorant. Now you’re more informed so ignorance isn’t an excuse anymore.