Is there any mention regarding manual labor in Manu Smriti?
See verse 7.138 on how a king can collect taxes from people who support themselves by personal labor.
Mechanics (kārukā) and Artisans (śilpi), as also shudras who subsist by bodily labour,—the King shall make each of these work for one day every month.—(138)
Medhātithi’s commentary (manubhāṣya):
Those who live by any kind of art he shall make work for him one day each month;—as also those who 'subsist by bodily labour'—i.e., those śūdras who carry loads &c.—(138)