If you update to DP4 directly before installing twrp you will be stuck without twrp.
You need USB pendrive and otg for it.
1. Update your phone to latest available official version.
2. Boot to fastboot and install TWRP (of course you need boot loader unlocked)
3. Flash DP4 from Thumbrive (keep it in external storage only)
4. Flash Recivery TWRP.zip from thumb drive
5. Reboot recovery
5. Flash DP4 again followed by Twrp.zip
6. Reboot recovery and flash magisk and any other mods you need.
If you followed every steps correctly you will have working TWRP and root on DP4.
I am using it since DP2 and never had issues.
Note. Since Q diesnt allow twrp to read internal storage you will need usb drive for flashing mod also.
I have uploaded a video with DP4 Features if you want to know about its features.
1. Volte working
2. Names of themes changed
3. System UI settings changed
4. Fingerprint faster
5. Overall phone is faster now.
Removed google assistant swipe shortcut.
Video link here