44, 6’3”, 85kg, Runner and Strength Training - what do you suggest?

Be gentle guys but feedback would be great - I turn 44 in March, endurance runner (marathons and trail runs) doing my second Hyrox in May. Always seem to have the problem of my running evaporating any muscle gains I make/maintain. 6’3 (190cm) and fluctuate between 85-87kg and currently around 12%BF.