I have just published two more encounters/mini-adventures on DMSGUILD both PWYW and both are probably good starting adventures for new DMs. I personally think The Marines is the best for a new DM as it is specifically designed for a bunch of first level fighters so that keeps things pretty simple to start with. Here are both of :
https://www.dmsguild.com/product/415891/The-Marines (1 page DnD Encounter)
https://www.dmsguild.com/product/415901/The-Hunters (1 page DnD Encounter)
Dungeon Bard 