Advice for a noob about speedfarming and GR's

So I just started playing d3 for the first time last week on switch and having a blast so far, but I have hit a wall in the season, I did the seasonal journey and got my set and got to about GR 60 but now things have slowed to a crawl and having a hard time grinding GR's, So i wanted to ask what difficulty should I speed farm and any other tips for progression will be great. (Also trying to work towards to this [build] (https://www.icy-veins.com/d3/lon-singularity-necromancer-bis-gear-gems-paragon-points) to help me push but having a hard time getting pieces to drop for me)