You can try Analog Dessert scripts
https://forum.cockos.com/showthread.php?t=241546
If you want to use specific font like Helvetica Neue, there is another way to change fonts in Reaper, but it doesn't work for all windows.
1) install a resource editor, for example Resource Hacker by Angus Johnson
2) open reaper.exe, select Dialog folder, in Actions / Save [Dialog] group to an RC file menu (namely RC, not RES, and only dialogs and not "everything")
3) open the saved file in a text editor (better "programmatic", for example Notepad ++), replace "FONT 8" with "FONT 10" (for simplicity in the entire file)
4) open modified RC in the resource editor, compile (Action / Compile Script) and save in RES
5) again opens reaper.exe, Action / Add from resource file and select our RES. Set Overwrite and Check all then click Import. Save modified reaper.exe
I use both methods, first Resource Hacker and than Analog Dessert scripts.
Example:
https://drive.google.com/file/d/1sTA...ew?usp=sharing