@Matt18 wrote:
I would like to sell QQQ and buy QQQM. These ETFs are identical except one has a lower expense fee. Will this trigger a taxable event for capital gains?
Yes. Even selling QQQ and then buying QQQ would trigger a taxable event for the purposes of calculating a capital gain.
Note that a loss would result in wash sale treatment (i.e., a loss would not be immediately recognized).