The issue here is that Roon treats the curly and straight apostrophes as different characters. If you look closely in your screenshot, the album titles use straight ones but the focus filter text uses a curly one.
It seems that you are using an iPad. The setting that makes the apostrophe curly is in iPad settings > General > Keyboard > Smart Punctuation. If you turn this off, typing will use the straight apostrophe and the focus will work.
It’s very arguable that Roon should treat them as equivalent.
The issue is the same when using the funnel filter. And also the same with double quotes.
Somewhat interestingly, on the Macbook I have smart quotes enabled as well, but they are not actually being used in Roon (nor in many other apps e.g. Safari - but they are used e.g. in Pages). Hence, this does not present an issue on macOS.
I believe the same issue occurred in the second screenshot in this old post, but it was masked by a different issue and got overlooked: