Generally speaking, sight reading training requires that you practice a lot of pieces that you can predominantly read successfully. Sure you can practice reading with harder works (you can apply for example some simplification like ignore rhythm and tempo to increase note and fingering accuracy) but the bread and butter improvement comes from doing a tonns of easier pieces and read a lot every day. A large part of sight reading training is being able to source pieces that you can successfuly control and which ones start to challenge you more (that means they offer a manageable challenge not a crazy hard one).
Simply reading a lot of works well will improve you and eventually you
will find certain repertoire paths which increase difficulty but are manageable and understandable thus your level of reading slowly raises up. Of course you will come across many small changes which totally confuse you and these are also valuable points of information for you to determine why they cause you so much challenge.
The largest challenge for the majority of readers starting out is playing the correct notes with the correct fingers, so reenforcing standard patterns such as scales, chords, arpeggios etc are not a waste of time so when you see them in pieces you are familiar with the routines and not "recreating the wheel" each time you read something. Being able to listen to yourself while you play and anticipate what sound comes next is also something that is challenging for many who start out reading since they are so involved with getting the correct notes and fingers, but if you read pieces that are easy enough you should be able to feel this flow of correct fingerings and notes along with being able to actually listen to what you are playing with some freedom.
Sight reading help? Book? Series? any other resources?