Due to life there are times when the only option for training is solo training.
Free video resources are linked at the bottom of this page

Solo training is far from optimal compared to having partners and it does limit your progress. However, it can greatly improve or speed up your progress in BJJ when you return to partnered or team training. Plus supporting health, mobility and conditioning.

From my experience, both as a white belt and after a few years of training, the main benefit of solo training comes from three sources:

• Movement training - BJJ specific solo drills
• Mobility training - BJJ Solo drills, yoga, calisthenics, equipment assisted exercises
• Cardio training - Running, lots others

Movement training is for both your body and nervous system to perform movements that are useful and common in BJJ rolling but less emphasized or uncommon in other activities. Examples include, shrimping, back-stepping, and technical-stand-ups. By focusing on this aspect of training, beginners will especially see superb improvements in their overall progression in BJJ when they return to partnered training.

Mobility training is for exercising your body to preserve or increase your flexibility while maintaining healthy strength and stability at full range of motion.

Cardio training is for endurance during rolling, which yields both muscular energy to perform for longer, and frees up mental energy to think and apply tactics. The old adage of "Cardio is King" has a lot of truth to it, if you don't have adequate cardio then your other attributes don't matter. Of course, skilled movement and strategy can make you more efficient and help supplement your cardio.

Strength training in moderation gets an honorable mention due to benefits for injury prevention and general health but personally it's not been a point of emphasis. If you are interested in BJJ and strength training then I can at least give some recommendation to Chewies Grappling Power or BJJ Strength.

Free Resources

Movement training:
YouTube Playlist: BJJ Solo
Chewjitsu BJJ Drill Playlist
Little solo drill I made

Solo drilling instructional by John Danaher (free at the time of the COVID-19-virus closing)

Mobility training:
List of YouTube channels which includes Yoga, Calisthenics, and Physical Therapy.

Cardio training:
Go for a run or better yet, interval training (e.g. walk 2min, run 2min, sprint 30sec, repeat, or use different patters or landmarks for distances at different paces).
Do the BJJ Solo drills with less rest and perhaps more intensity for time.
Etc,... etc,... etc,... Endless others of course.