I ran Plesk on an old VPS many years ago, when I think it was version 11. It was the worst thing I’d ever used because it made everything I tried to do extremely difficult. Whenever I wanted to do something, nothing I found on Google seemed to work with Plesk. Plus, the Plesk support community is practically none-existed or aimed at people much smarter than me.
After getting rid of that server everything became so much easier - And all of the help I found on Google finally worked.
All I know for sure is that Plesk uses some sort of vhosts setup (as you mentioned) which it generates when setting up new sites. You might be better trying to find and edit the relevant file from within Plesk rather than directly within SSH. Again, if I remember correctly if you edit those files directly then Plesk can overwrite your changes because it uses the settings in the Plesk menu to generate those files.
Sorry, my answer wasn’t what you were hoping.
Disclaimer: It was a long time ago and my memory is hazy at best.