I can't paste a text or a link on mobile when it is not a quick reply form. In blogs there is no quick reply, so i can't paste anything in the blogs (same on older Android 5 device and new Pixel with stock Android 9, stock keyboard, stock Chrome). When i long press, Paste menu appears, but when i release my finger input window jumps around and paste button disappears. I have posted a video once showing that jumping which in itself alone creates a big annoyance trying to post anything here on mobile. I can post another video if you want.
Btw, i have to deal with this jumping all the time and it makes harder to start typing as view jumps out of bounds and i can't see what i type, so i have to carefully drag it back into view and it often jumps again and i have to repeat. This is not happening in quick reply form. Also for some reason in forums it is not loading editor for me on Pixel/Android 9 as it does in blog posts, so it works as with quick reply. But on Huawei/Android 5 it loads the editor so i have the same jumping experience in forums.