Any hacks for removing the residue of really stubborn masking tape from windows?

I used a ceramic hob scraper but be careful you use it at the correct angle or you will scratch the glass. One like this and then your liquid of choice with it.

https://www.amazon.co.uk/1-x-Minky-Hob-Scraper/dp/B07WSXVKFD

If you've got any WD-40, try applying that with a cloth. That should work.

Or try using vinegar and bicarbonate of soda. I use that mix on lots of things.

Point a hairdryer at it. It heats the glue and you can gently scrape it off.

WD40.

^ This. Whiskey Delta forty is your man.

I wonder if petrol WD40 or any of the other suggestions would affect it, who knows.

It looked like an old wooden framed window to me which I presumed was single glazed, maybe I'm wrong but the OP knows what he has so can decide what to use. My bad if I'm wrong and it could damage it.

Thanks for making that crystal clear, sorry for the pun!

Theres no hack, there's just the way!

You want this stuff, apply, leave for 5min and then remove residue with a soft plastic scraper or cloth.

https://ie.rs-online.com/web/p/adhesive-removers/0491724?cm_mmc=IE-PLA-DS3A-_-google-_-CSS_IE_EN_ePmax_Prio3-_--_-&matchtype=&&s_kwcid=AL!14853!3!!!!x!!&gad_source=1&gclid=Cj0KCQjwo8S3BhDeARIsAFRmkONVjvCwD0fo8WB5ousesEQ0zFFuYBNnXH4BKUogPPiYBGwh2_8awMQaApuYEALw_wcB&gclsrc=aw.ds

Did you try the petrol?