Adding sub panel, odd main panel configuration
The black strap behind the main breaker ties the two neutral bars together

According to the wiring diagram on your panel label and the photos you posted, the inter-neutral tie in your panel is performed by the black insulated strap that sits behind the main breaker.  This configuration is relatively common for loadcenters, and works relatively well for keeping the inter-neutral tie out of the way when dual neutral bars are used.

The bonding screw is on the left side, but looks like it needs to be tightened.

The bonding screw on your panel is the 13th (yes) small screw down on the left side neutral bar.  It appears to be present in your photos, although backed out --  turning off the main breaker, tightening it down firmly so that it makes good contact with the cabinet, and turning the main breaker back on again will cure that issue and provide you with a solid neutral-ground bond at your panel.