I might be similar to you in how I play. I grab the 'blue' quest marks on the map as I come across them while doing the main scenario quest, also known as MSQ. I wait till I get to a point in the MSQ where I need to do a run with a group. While waiting for the opportunity to group up with friends to deal with the MSQ in the Duty Finder, I use the down time to work on the quests I received from the 'blue' quest marks. Every 'blue' quest leads to an unlock instance in the Duty Finder. You want to make sure you did not miss any of the unlocks.
If you want to make sure you have not missed any quests that lead to Duty Finder unlocks then check out the resource I linked below. The resource is tested true up until Shadowbringers, as any game content beyond that are not listed.
As you visit each page, notice they are the same portal, and that there is a menu to the left for other helpful FFXIV topics.
That's all the guidance I have for you today.