just give your phone a fresh clear cache
1. turn off phone
2. connect to a PC or USB headphone
3. press and hold power + volume up keys
4. release the hold when you'll see a logo
5. press volume down to select "clear cache"
(do not select clear data as will erase all your files)
5. press power key to confirm
6. press power key to okay reboot system now
Split Mode i belive has changed in the Android 11 Samsung One Ui 3.0 update i believe.
There are threads on the forum discussing this with one such thread being galaxy-s20-fe-galaxy-s20-galaxy/split-screen-on-galaxy-s20-ultra.
In regards to apps not working as they should I would suggest to first make sure they are updated in your Playstore and then go into Settings , Apps, choose the app, Storage and Clear Cache and if necessary clear Data.
Current Phone > Samsung Z Fold³ 5G. > Software : Android 12 ~ Samsung One Ui 4.
Originally the One UI 3.0 update for S10/Note 10 devices was pushed back to February, however it has now been pulled and we do not have a date at the moment when the update will resume. https://gadgets.ndtv.com/mobiles/news/samsung-galaxy-s10-series-android-11-one-ui-3-0-update-roll-ba...
Obviously disappointing, however the bugs need to be sorted out.