I enjoy multimodal solo touring. I retired early so my younger adventurous friends are still working, and my older retired friends (and wife) are not interested in sleeping on the ground anymore (none are bicycle riders). I'm also interested in rather specific niches that makes it difficult to match partners.

For me, Kayak touring is the only thing that requires a partner as water can kill quickly in a number of ways. For solo backpacking and motorcycle/ADVtouring, I use an Inreach Satcom/locator which provides 2-way comms anywhere, and breadcrumbs my trail on the web for the Mrs. to follow - if my trail stops for too long without a message, she knows something is wrong and exactly where I am. For long distance, I tour with an RV/campervan (and take my dog) and generally within cell service. I like bicycle touring in more densely populated areas (Eastcoast/shoreline) where a bicycle is advantageous and use an ultra-compact rig to address the security issues (take everything inside).

As others have mentioned above, I enjoy chatting with others along the way - on the road you are never really alone, and strangers will go out of the way to help you if you are in trouble. Even solo backpacking, where you can go days without seeing another sole, is rewarding to me in an adventure/self-sufficiency/survivalist sort of way.