My trick with this - write down any BS you want to. I mean any crap at all. Such as your thoughts about the paper that the journal is printed on, or the ink in the pen you are using.
Eventually, your brain will decide to write down something worthwhile. Maybe not today, or next week. But some day. Until then, enjoy writing stupid stuff down. Like whether you liked your eggs scrambled today better than fried yesterday. At the worst, you are practicing your handwriting, on the off chance you actually have some earth-shattering insight. So you’ll be able to read it later.
My journal is full of utter nonsense. But I write in it anyway. I enjoy the writing. Makes me enjoy my journal as an object (I have a nice one) and my pen (a fountain pen - lovely tool). Some day I may go back and read it. 