I have a Galaxy S10 on Android 9.0 & One UI 1.1. I've been noticing that when I open the Galaxy Store and tap "My Page" from the top menu, and then "Updates" to see if any apps need updated, my app store will tell me all apps are up to date. However, when I search for "Samsung" Apps, I can see that my Samsung TTS app needs updated. I have auto update enabled for the individual app, and in my Store Settings. This happens with other Samsung Apps as well, the TTS app just happened to be the only one not up to date at this moment.
Have you tried Force Stopping and Clearing the Data on the Galaxy Store app? https://www.samsung.com/us/support/answer/ANS00077611/
You would want to clear the data, not the cache. Also, you can put the phone in Safe mode and see if the update shows correctly. You can also try clearing the cache partition of the phone.