When you spam click a respawn anchor in the overworld with glowstone, it blows up but if you click fast enough you can place a block where the respawn anchor that exploded was even though there is nothing that you should be able to place it on. I tried this in single player with no mods and it worked but it took a few tries:

https://www.youtube.com/watch?v=Kzo9Tu11w7w

I was doing crystal pvp and found this so i tested it in single player!