The wayback machine/archive.org is probably the safest bet, that isn't going to break any time soon. They currently have an active Reddit archive project going, so it's likely that your post might be captured on the archive (or you'd be contributing to it).
FYI all of these solutions stop working in 10 days 🤣
Wrong. Most solutions (see below) linked here are either proxies or scrubbers-archivers, which mean they are using HTTPS requests to access a web page.
If such solutions really stopped working on July 1st then you wouldn't be able to access reddit with your browser.
Which could be an interesting side effect.
(About teddit and libreddit: those two are "portmanteau" using varying techniques to obfuscate reddit crap. Teddit is indeed using some "unofficial" API so it may or may not work, and apparently libreddit is proxying requests so it should probably work. It will also depend on their .json use as it is also covered by the new terms.)