Thank you for the detailed report and for sharing your setup information.
To help us investigate this issue, could you please clarify which exact keyboard model you’re using with your OnePlus Pad 3?
It would also be very helpful if you could record a short video showing the delay and input behavior you described.
If the video file is too large to upload here, you can upload it to a third-party storage service (e.g., Google Drive, Dropbox) and share the link in your reply.
By the way, a similar issue was previously discussed here:
https://community.onlyoffice.com/t/mobile-app-on-phone-and-tablet-registers-inputs-very-slowly/11620/5
We’ll check if your case matches that behavior once we have more details.