Here's how I fixed my Roku 3 that was stuck on the Roku splash screen. Similar to you I came back one day recently to use my Roku, sometime in August 2025, and found it would not boot beyond the dancing Roku logo. Like others, I concluded that it had failed to update correctly, and its software was corrupt.
I resolved the problem by entering recovery mode on the Roku 3 and reinstalling the software, which is easy to do. You get a staple or paperclip and insert it into the reset button opening, being sure that you feel the button click. Hold the button down for at least 20 seconds. Your Roku 3 may reset when you first click the button, but hold it down anyway until it resets again. The Roku 3 will then boot to recovery mode. Next, you will pair the remote by pressing it's button under the battery door for 5 seconds as directed on the screen. Then, using the remote, you will follow on screen directions to connect to the internet, either using wifi, or ethernet. Once connected the software will download, and the Roku 3 will boot up and be unbricked. You may need to log into your apps again, but what else can you do. Just like that and Bob's your uncle.