Can the M1 MBP drive a 4K display at 60Hz when not in clamshell mode?
Yes, this is officially possible. Your MBP supports full native resolution on the internal display in addition to a single display up to 6K at 60 Hz.
To quote Apple's technical specifications:

Video Support
Simultaneously supports full native resolution on the
built-in display in millions of colours and one external display with
up to 6K resolution at 60Hz

M1 MacBook Pro 13&quot; - Technical Specifications
Italics added for emphasis
As you can see, the specs specifically say: &quot;Simultaneously supports&quot;.