You can install a 3rd party app from play store named as zfont. It has a lot of working fonts for One Ui.
If u want to install fonts like Rosemary, choco cooky and Cool Jazz without any 3rd party app follow the below instructions:-
1. YOU MUST HAVE ANY VPN IN YOUR PHONE PRE INSTALLED, IF NOT DOWNLOAD SEED 4 ME or ANY OTHER VPN.
2. REMOVE YOUR ALL SIM CARDS FROM PHONE. (MOST IMPORTANT)
3. CLEAR CACHE & DATA OF GALAXY STORE APP. ALSO FORCE STOP IT.
4. CONNCT TO ANY WIFI NETWORK.
5. OPEN YOUR VPN APP & SELECT COUNTRY AS UNITED STATES & CLICK ON CONNECT.
6. OPEN GALAXY STORE ONCE AND LET IT LOAD. ONCE IT OPENS CLOSE IT.
7. OPEN SETTINGS. GO TO DISPLAY >FONTS & CLICK ON DOWNLOAD FONTS. IT WILL OPEN GALAXY STORE. SCROLL DOWN. YOU WILL FIND ALL THE FONTS I.e. ROSEMARY, CHOCO COOKY & COOL JAZZ LISTED THERE. CLICK ON DOWNLOAD. ALL FONTS WILL BE DOWNLOADED & INSTALLED.
8. NOW YOU CAN RE INSERT YOUR SIM CARD.
& DONE. ENJOY. IF IT HELPS PLEASE LIKE IT & ACCEPT IT AS A SOLUTION
😍😊 ((((( solution given by Mr. ABHISHEK SINGH)))