Dungeons & Dragons can be a difficult hobby to enjoy in person, as it requires a group of four or five people to sync up their schedules on a regular basis. This self-isolation period, though, has prevented people from playing D&D and other tabletop games in person. Many fans have taken to enjoying the game on stream. However, for the people who cannot find local friends or online players, there are solo D&D adventures that can be purchased online.
The 5E Solo Gamebooks page on the Dungeon Masters Guild website has a number of solo adventures that people can enjoy on their own. All they need is knowledge of the rules/the Player's Handbook and some dice. Each adventure is tailored towards a solo character of a specific level, so the player has to prepare an adventurer before they can start.
The solo gamebooks are similar to the old Fighting Fantasy gamebooks from the '80s, except that they are tailored around the current edition of Dungeons & Dragons. They come with an adventure book and a map book. The player starts with the introduction of the adventure book and moves to different entries based on their decisions. These entries are written with combined words (like SPIDERBATTLE) to make them easy to search for in a pdf without having to scroll through the other pages. The book also has hotlinks to make it easier to jump to the correct entries. The books do a great job of predicting the kinds of solutions that players could think of, such as using class abilities or making skill checks, so the players have more options than in the gamebooks of old.
The map book contains several small tile maps and the player moves between them based on the numbers at the edge. Combat encounters take place on these maps and the player is expected to control both their character and the monsters. The developers ask fans to always run the combat encounters fairly and to act as if they were the DM, in order to keep things challenging and interesting. The adventure book contains the stats for each enemy, so the player doesn't need a Monster Manual to run the gamebooks.
I tried out The Death Knight's Squire, which is an adventure designed for a level 2 character. Fortunately, I had created a level 2 dragonborn cleric of Waukeen named Zarlandris for a recent game and he was ready to go. Unfortunately, poor Zarlandris died in the first combat encounter, as he ran afoul of some giant wolf spiders. Zarlandris never made it out of the woods, but maybe your characters will have better luck on their own solo adventure.
Source: 5E Solo Gamebooks