One of these things is not like the other. That's a 3/4 gas outlet and a gas dryer with a 1/2" fitting. What's the best approach to making them connect? The dryer is old so I'm a bit leery of trying to unscrew the 1/2" adapter at the appliance side.
If you don't want to remove the 1/2" adapter from the dryer you will need a new supply line that has the correct size. I don't like using intermediate fittings but prefer the the correct size fitting on the flex as this reduces the possibility of a leak.
Just remove the old adapter (you may want a backup wrench) there isn’t any reason the old connector shouldn’t come off. Replace it with one that fits your gas flex and you are done. The adapters are usually fitted with 3/8” NPT on the inside and 1/2” NPT on the outside. It looks like you are using the 3/8” NPT. Just a note about gas flex connector sizing, some manufacturers use ID and some use OD. It looks like you have a 1/2” flex with a 1/4” fitting which would be called 3/4” flex with a 1/2” fitting if going by the OD. Just something to watch out for when purchasing adaptors and gas flex lines. When deciding which flex line to get it is listed on the flex itself how many BTUs it can handle for a particular length. With some driers some longer 1/4” (1/2” OD)gas flexes will not be adequate. I generally go with 1/2” (3/4” OD) for driers to avoid any problems later.