What is the genre of Let Go?

To me it's pop, not bubblegumpop or mainstream pop but it is pop

Pop rock, leaning more towards rock than pop.

I think it sounds a little bit different from pop rock, and these songs that I listed have a very strange sound instrumentally. Does anyone know similar songs not by Avril?

Pop rock is more like TBDT, don't you think?

Avril herself has always referred to LG as being pop/rock and has always referred to herself as being a pop/rock artist. Her music has generally always been a mixture of pop and rock, so I don't see the issue with calling it that. What else could you call it?

If anything, the sounds you're describing are still derived from pop music. Pop is not restricted to just computerized beats or synths, stupid lyrics, or electronic sounding dance music. A song like Somewhere Over the Rainbow is considered to be a traditional pop song. I'd say songs like ABO, My World, Tomorrow, Things, etc. are all pop or pop rock songs. It is just the production they chose to use that makes them sound unique and interesting. The only true rock songs on it are Losing Grip and Unwanted, and maybe Too Much To Ask.

It's just that I'm searching for songs that are similar to the songs on Let Go, and I can't find any.

Anyway, I think I'm convinced it's pop rock now I just thought pop rock was a little bit different.

Chances are that you won't be able to find songs that really sound similar but you can certainly find similar artists. Maybe check out Michelle Branch, Skye Sweetnam, and Katy Rose? The closest you might be able to find are other female pop rock/singer songwriter artists that were around in the same time as Avril.

Listening to LG now and it's strange how much heavier and guitar based it and UMS are from what I remember. Her basic production has become much softer and more pop. It's a shame.