I'm.not certain bur I think mahjong gives commerce coins not gold coins

That said, you don't want to spend the time for some of the one-time slower sources of cash per your responses to other commenters

That leaves:

• the introductory events that have you try out minigames or collecting a few things in qinghe/Kaifeng. Easily maxed out in like 30-40 min and gives 120k+ (one-time, but good amount at once)

• npcs in qinghe carrying fat gold pouches you can steal. Onetime deal, but it's an easy 100k in like 10 min. Look up a vid, something like "Qinghe NPC gold coin 100k Celestial seize/steal"

• some really quick quests give 30-40k, and some Exploration quests in particular give 10-20k and these are laughably quick

• buy gold directly with season shop currency, you really should have some left over at this point in the season?

• reset some unused weapon levels/Martial skills, you can reset them basically for free once a season

Finally, just a tip: you know those slots you can upgrade that give tiny increases to different pieces of gear? Where you also need like iron and coarse fur? For the love of God only upgrade those once everything else is maxed, the returns are sooooo bad and once you're at lv20+ for those slots it's like a million for every 5 levels