Did TLJ backlash have anything to do with underperformance of SOLO?

No, this flopped on its own.
They took a great character with lots of potentially interesting back stories and made it dull.

Yes.

That and the movie was crap.

Possibly - I haven't seen a Star Wars film since. But then I was never going to go and see this particular film anyway.

No bc to general movie going audiences TLJ wasnt seen as the wildly polarizing movie that online/sm made out to split the fan base to the bone . Its just Solo looked 'meh'. an origin story of the iconic Harrison Ford character without Harrison Ford? Bit like a Han Solo version of The Young Indiana Jones Chronicles. No ones that bothered unless its actually him in it (obviously SW prequel backstory movies had been done before e.g. young Obi Wan in TPM but that was a different thing as it was "Episode I" of the saga not a character tale movie, and was long awaited 4th movie. and Rogue 1 just looked an amazing SW film which that featured Vader and the original Death Star and all the XWings/tie fighters etc that tied in directly to the original film)