Sound bars don’t have a lot of fidelity that can be lost. Even if you had a 10% drop in fidelity using an HDMI splitter no one could perceive a difference.
fwiw I used an HDMI splitter several years ago in an HT system for a few weeks. I had bought a new component that required HDMI and my AVR, which was several years old at that point, was one of the first to have HDMI inputs but only two, and this was the third component requiring HDMI. I used a splitter and then purchased a newer receiver. I really didn’t notice any issues while using the splitter with the older AVR
fwiw I used an HDMI splitter several years ago in an HT system for a few weeks. I had bought a new component that required HDMI and my AVR, which was several years old at that point, was one of the first to have HDMI inputs but only two, and this was the third component requiring HDMI. I used a splitter and then purchased a newer receiver. I really didn’t notice any issues while using the splitter with the older AVR