This happens EVERY day to EVERY web server out there. I have a personal site that gets thousands of requests per day from bots.
Running a public server (like NTP) means you will get tons of strange requests. Moreso if you run a web server on the same IP because bots will scrape certificate transparency logs. The entire IPv4 space is scanned continuously.
This may sound harsh, but you cannot stop it. It is whack-a-mole. Filter it and move on, go outside and touch grass, seriously. This is not worth being upset over.
I treat these as an opportunity to tune my filters and firewall rules.