Minecraft Speedrunning/Other Structures
There are quite a lot of miscellaneous structures which are useful for minor things but aren't common or useful enough to be a staple in a speedrunner's repertoire. Still knowing some things about them can be useful in some situations.
These spawn underground and have chests in minecarts which can contain food and iron. They spawn most commonly and are often exposed in mesa biomes. They have cave spiders inside which will poison you if the difficulty is higher than easy.
These spawn in or near oceans and can have stone axes and buried treasure maps but are otherwise not very useful and you will often get attacked by a drowned.
Also called desert temples, these spawn in deserts and have some useful resources like golden apples, iron, gold, diamonds, string and 9 tnt. Definitely can be very useful although they tend to not have quite enough iron or food and take too much time to loot to be a mainstay of speedrunning in 1.16.
Igloos spawn in snowy biomes and will contain a furnace. Half of igloos spawn with a basement section which contains a golden apple and a splash potion of weakness for curing a zombie villager which gives good trades. This would be useful for the trading with villagers for ender pearls strategy, but this strategy is slower in 1.16.1 than bartering with piglins. Also can contain a stone axe in the chest in the basement.
Jungle Temples spawn in jungle biomes and contain 2 chests, one hidden behind the lever puzzle and one behind some dispensers with arrows. Can contain some iron, gold and diamonds but are quite inconsistent. Oftentimes, mining through the lever puzzle and accessing the chest this way is much faster than solving it.
Pillager Outposts spawn in the same biomes a village can spawn in. They have one chest at the top which can contain some iron and logs as well as some food. They can also spawn with a caged iron golem, but killing the golem while being harassed by pillagers is very difficult.
Swamp huts, or witch huts are basically useless for speedrunning since they have no chests. Theoretically one could obtain a useful potion by killing the witch at the right time, but this is very inconsistent and not very applicable.
Woodland mansions are actually quite useful but they are so rare as to not really be worth investing time into. They also can take a lot of time to navigate because of how large they are. There are many different rooms and lots of loot from chests. Here is a semi-serious guide to mansions made by T_Wagz.
Dungeons can have iron and buckets and some food in their chests so can be useful but as with most underground structures they are somewhat rare to find.