My site has slowed down a lot, please help.

[TangledPubes]

Hello everyone, Easy work! I'm not sure if it's forbidden to put a website link, but if it is, please let me know. Our website is hesapsat.net, a classifieds site. Until about two weeks ago, the site's speed was quite normal. However, the speed has significantly decreased over the past 2 weeks; the site has slowed down a lot. Last week, there were even instances of a 504 timeout error. The site has a server (Plesk). Can anyone who knows the reason behind this issue and its solution please assist me? We have lost a significant number of members and visitors in the past 2 weeks. By the way, the traffic area, etc., are all unlimited. I await your help, and wish you all a productive day.