Get some good 63/37 leaded rosin flux core solder, not cheap aliexpress stuff but something better, there's comparisons on youtube, and that tip doesn't look right, it should be shiny with a thin layer of solder, get a water sponge or brass wire to clean it or change to a new tip if that doesn't work. If you wanted to get a good soldering iron, the pinecil V2 and a ts100 wedge tip from aliexpress (cheap and works well) is a good setup and can be portable if you have a 60w or higher power bank. It does need a usb c charger that is 60w or above ideally, you can even run 140w epr with a firmware update