Dungeons & Dragons has a new way to allow for one player and one DM to attempt some adventures within its new Dragon Delves anthology. Out in early access now, Dragon Delves features a new supernatural gift called "Blessing of the Sole Champion" that is meant to aid solo players in playing through some of the adventures in the new anthology.
The blessing comes with the following attributes:
Heroic Inspiration. You gain Heroic Inspiration when you finish a Short or Long Rest and whenever the DM has you roll Initiative.
Temporary Hit Points. You gain a number of Temporary Hit Points equal to 10 times your level when you gain this blessing and when you gain a level.
Three adventures in Dragon Delves are marked as being appropriate for solo play. They include the Level 3 adventure Baker's Doesn't, the Level 7 adventure The Dragon of Nakjir, and the Level 12 adventure A Copper for a Song. All three adventures feature an emphasis on non-violent problem solving rather than traditional dungeon crawls or repeated combat encounters. However, there is some combat in each adventure.
Support for solo adventures are somewhat rare. The last product to support solo play was the D&D Essentials Kit, which introduced scaled-back companions that the player could control to fill out their party. Companions were further fleshed out in Tasha's Cauldron of Everything but have not been featured since.