My ears pricked up when Giles Mcmullen suggested that while reading you close the book after every page & write down everything you remember. I've been using this with a rather dense book on Frank Lloyd Wright and I'm more engaged with it that I could have hoped for.
There are other great suggestions in his video to consider trying:
I also recommend buying a big-ass bludgeon sized dictionary and leave it open to the side as you read. Look up every word you aren't 100% on.
Additionally, have an LLM accessible. Sometimes you re-read a sentence, you re-read the paragraph, you look up words, & it still doesn't make any damn sense. I got stuck on "proleptic history" today. Keep asking the machine to explain until you get it. Then continue reading.