Hey Jay,
Welcome to the forum! 
I don't have good access to any version of macOS later than Mojave at the moment.
This might work on the Big Sur version of Notes.app.
tell application "System Events"
tell window "Notes"
tell splitter group 1
tell splitter group 1
tell group 1
tell scroll area 1
tell text area 1
set focused to true
end tell
end tell
end tell
end tell
end tell
end tell
end tell
If not you'll have to try to figure it out for yourself:
See this thread:
Front Window Analysis Tool Using AppleScript System Events (List UI Elements)
See UI Browser.
-Chris