I noticed this problem long ago and might have even posted about it before. It occurs on the Roon desktop app with any large album with many tracks, and gets progressively worse with larger number of tracks.
For example, the album Decca Sound: The Analogue Years 1954-1968 (available on Qobuz and Tidal) is 54 discs and about 300 tracks.
If I type “mozart” all at once into the filter field, the letters slowly appear one by one and it takes about 20 seconds before it is completed (running on my 5 year old Intel MacBook Pro). On my very old Lenovo ThinkPad laptop running Windows, it is even much slower. So it is a problem with the Roon desktop app on both Mac and Windows.
However, it is not a problem with the same album on the Roon mobile app (both Android and iOS). There is no lag and the response is almost instantaneous. Desktop and mobile should be doing the same thing to perform the filter function, but there is something very wrong with the desktop version.