Can I resume normal activities, such as lifting (I have a strenuous work life) 3 1/2 to 4 weeks after hiatal hernia surgery’s (laproscopic)?

Give it more time. One of the causes of early hiatal hernia repair failure is sudden increase in pressure inside the abdomen like coughing, vomiting, lifting heavy stuff etc
Body takes 6 weeks roughly to lay down the matrix needed for healing, tissue continues to heal for months afterwards but at 6 weeks after surgery it has reached 80% strength. Running jogging should be ok at this stage .