If you end up buying some flux then I’d recommend you also buy and try a block of violinist rosin:

www.ebay.com.au/itm/315948528490

You break it up and then dab chunks onto your joint whilst soldering. Some will melt off and then burn. From there it acts just like any flux: reduces the metal oxides, makes the solder suddenly flow (behave) a lot better and provides some level of temporary oxygen shielding with its off-gassing products.

Pros:

• Cheap
• Doesn’t smell awful
• Long working time (easy to use)
• Very simple ingredient (distilled pine tree sap) made by many manufacturers, so it will never go out of stock.
• Residues are non-conductive and can be safely left on your boards
• Residues are reasonably easy to clean (isopropyl & most board cleaners work; ethanol also works but tends to leave ugly white streaks)

Cons:

• Smoke is still harmful (smoke = incomplete combustion compounds)
• Residue is dark, unlike the transparent residue of many no-clean fluxes, so it can hamper inspectability for mass manufacture.
• Best handled with tweezers, otherwise your fingers end up feeling sticky (pine resin compounds are slightly sticky)
• Not Modern or youtube popular, so people will tell that it’s therefore bad or worse than other products.

I use it often, it’s my favourite for both big joints and fixing smd work. Grab some and try it :) The worst you will be out of pocket is a few dollars.