all windows 10 Folders will have this (Attrbutes) Read only (Only applies to the files in folder)

if ya right click any random folder you will see that..

did ya try what leocg said - (Try checking if the file is not locked and that Opera has the right to write on it.)

try this also while opera is closed - make a back-up copy of that history file and then open it with notepad

after ya open it - scroll down to the end and - add some text to it - save it in the same location as the original history file - same file name

then re - open the file you edited to see if it saved your text ya added..

if ya see your text most likely the file is not Locked and opera should also be able to edit the file too (remember to put the original history file back when done)

to check n e programs for 32 or 64 bit
open taskmanager - details tab - rigt click and choose columns - scroll down and check box for platform..

You can also try installing Opera portable and check if it also has the issue.

btw what version number of opera and is it 32 or 64 bit..

also CCleaner and other apps like that clean history.. but i doubt that being the culprit..

and or - if your use 'n (New Private Window) if so.. then when close 'n all private windows.. opera will clear the follow 'n associated data - browsing history, items in cache, & cookies..