I'm using a Lenovo a2010 running a (unofficial) build of Resurrection Remix right now (I'll try the stock rom later), tried both methods but they both failed. The problem isn't the keyboard though is the OS not displaying any emojis at all when using this font (the ios 11 one works just fine)
If you search with a root explorer in the root/system/fonts folder is there a notocoloremoji.ttf there? If not I suggest replacing that manually with whatever notocoloremoji.ttf u want taken from /system/fonts inside the Magisk zip. Safetynet will get triggered though but it probably already is if that file is indeed missing.