You can generally add "-" before a domainname for search engines to prevent content from that domain showing up.
So for reddit, you'd search "weather -reddit.com". It should work. This is short and generally works but If it still shows up "weather -site:reddit.com".
you can also add multiple domains like "-reddit.com -stackoverflowclone.com -seojacked.com"
You can also do this by default using custom search engine with a search string that already contains the domains you don't want.
For ddg: