[2023] Making legendaries

So I'm new to the game, only about 30 hours in it, and I don't really look anything up. So I just simply read using the tool tips (which is the best/useful tooltip system out of any arpg I've played) how to make a legendary item using LP, did the dungeon and got to the eternity cache...but then just couldn't use it. I didn't realize that the item had to be the same exact type (and subtype as well, so not just ring to ring but ruby ring to ruby ring). I felt deflated afterwards because none of my uniques matched with my exalted items so I essentially just wasted the key and left empty handed.
It feels hard enough getting an exalted with the right set of affixes on it that are relevant to your build, and also to find a unique that has legendary points that is also related to your build. Does this get better the deeper into mono's I go? Will more uniques drop with more LP on them and do more exalts drop?

In my naivety I feel like you should combine any legendary with any exalt that you want, since the creation of a legendary may not even get you the affix you want. What do you all think?