This section of pipe has looked the same for a few years (perhaps the whole time I’ve lived here)Never seen visible leak or dampness. So am not sure if this is a leak or impending leak……does this warrant a plumber visit to replace section of pipe?
Looks like the flux from soldering was not cleaned off throughly, and then the pipe was painted.
Scrub it clean (which will take poorly attached paint) and possibly use a bit of sodium bicarbonate to neutralize any remaining excess acid from the flux, then rinse, then (if desired) repaint (or don't if not desired.)
No plumber should be required.