Not OP, but I have this same issue on a OnePlus 7 Pro with Android 11, using Gboard in English. Interestingly enough, it doesn't happen when using Gboard in Korean or Chinese.
Also, if I tap on the end of a line and press newline, I get another block. If I type something and then press newline, then it happens exactly as ronyeh described (again, only with Gboard in English)
Once I got the hang of a default world, Death World was an extremely satisfying challenge. It helps me to not get stuck trying to perfectly place my iron smelting line because I have to get it down now or else the biters will destroy everything.
Also, if I tap on the end of a line and press newline, I get another block. If I type something and then press newline, then it happens exactly as ronyeh described (again, only with Gboard in English)