Wildcat Progression Theme update

Hi all,
Recently I have updated my website www.opdroomreis.nu to WordPress 5.5.2 (and this week to 5.5.3). However, ever since it doesn’t show drop down menu’s anymore (using PC/laptop. Mobile phones are fine). I have been told my multiple people this has to do with my theme; Wildcat Progression, from Themeforest. This was purchased in 2016, and doesn’t have an automatic update in WordPress. Therefore I am still using version 2.0 which seems to be not compatible with WP 5.5 and therefore creating problems with the drop down menu.
The only thing I have got from this purchase (done by someone else who created my website, and could only find the below information) is the Item Purchase Code.
How on earth can I update my theme and get my website (with almost 200 pages content) running again?
Thank you very much for your thoughts!
Kind Regards, Judith