Solipsism is easy. The universality of doubt can only be a starting point. Yes you've stated that we're not 100% certain of X but also that we're not 100% certain of anything. This alone would simply put X in the same category as everything else in the entire universe. However our degrees of knowledge are not so black and white. Can we not say that though we cannot be 100% certain that Ted Bundy was a murderer we can find more reasons to believe it than to believe that the tooth fairy is real. Different claims have different qualities of evidence supporting them. The question of whether we can be 100% certain of something can be a meaningless distraction unless we build upon it to ask how reasonable it would to doubt it. How much evidence, and what quality of evidence would we need to discount in order to apply such doubt.

Yikes sorry about the typos. A mixture of iPad typing and Siri. Embarrassing.

Yes one can never be 100% sure of any contention being true or false under all circumstances.
For example under laboratory conditions, a group renowned scientist could leave milk and cookies at the base of a chimney in a house where "Nice list" children live every christmas eve for one hundred years, and then measure the resulting consumption and monitoring the following morning.
IF in 1% of cases, the cookie is nibbled and the milk sipped, IF on 1% of the cases a jolly fat man with a sack is recorded coming down the chimney and making off with the Blu-ray player, it still does not prove the existence of Santa, (as a mystical being or as a burglar) is proves there are unaccounted variables.
Because of such a study I am not going to leap at the one % and start becoming an ardent Santa-ist again hoping to be, one day, a good enough boy to wake up one December 25th with a stocking full of goodies in the fireplace, and I am certainly not going to reinstall a coal fire and chimney for especially this purpose as an act of faith!

“You can never be sure 100% that there isn’t a ” is the argument from desperation, the last act of a drowning man clutching at a razor blade.
It is the scientific equivalent of the sulking spoiled kid, sticking out a pet lip, stamping a foot and sulking because they can't get their own way.

Scientific reasoning is never 100% sure. It is always open to new evidence. Religious reasoning is 100% sure and is not open to any evidence.

When the evidence is that something is 99% in not existing it's still better to rely on the 99% than the 1% . It's 99% that you will get hit by a car by crossing the road at point A do you rely on the 1% and still cross ?

The fat thing od virus has struck again stealing your th ins.