I know lots of conservatives who aren't religious.
No, Sanders would never be a unifying figure. Libertarians see him as being essentially equivalent to Trump: a demagogue who makes emotional appeals to build a cult of personality, deeply misunderstands economics, and seeks to use political power in an unbounded and illegitimate ways.
They are noise in the data.
Populism is a marketing tool (to quote Hank Green) and Sanders wielded it as well as trump, but to help people, not punish them. Both have decades of track records demonstrating this fact.
Various surveys have indicated that 20-30% of the US population broadly align with libertarian principles, regardless of party affiliation or nominal identification. This aligns fairly well with the proportion of the electorate that had negative opinions of both Trump and Harris in the last election (even those who took a "lesser of evils" approach and voted for one of them).