The internet is NOT permanent - it's up to YOU to archive it

Contrary to what you may have heard, content on the World Wide Web is not permanent. Chunks of it disappear every day, even from the so-called Internet Archive which readily removes "archived" content for a variety of reasons, not all of which are legitimate or ethical. The service also requires visitors to have an account in order to view content it deems controversial, though such content is often factual information which is anti-establishment in nature.
When you come across a web page you want to save, the most obvious solution is to press Ctrl+S and your browser will guide you through the process. You can save textual and image content this way, but not embedded content such as audio or video. If you want to streamline the process there are browser extensions you can install. For instance, the Firefox add-on repository (AMO) has several extensions you can use to save content, one of them being SingleFile by gildas.
Saving video is another matter and while there's a plethora of browser extensions that may accomplish the task, i would suggest being very careful about what you choose to install because they may contain malware (tracking, ads, data slurping, etc.). A much better alternative, in my opinion, is to install the open-source, multi-platform yt-dlp program which is a fork of the older youtube-dl. Binary releases are available for most operating systems, but if you're running a Linux OS you may find it in your assigned software repository, though the disadvantage to installing this way is not being able to easily update it in a timely manner when a new version is released which happens often. Unlike its name might suggest, yt-dlp is capable of downloading videos from almost any video hosting platform or web page.
Downloading videos with yt-dlp is as simple as copying the video page URL and issuing the commend yt-dlp <video_page_URL>, however the program offers a ton of advanced options for fine-tuning everything imaginable. The wiki is a useful resource for those wanting more from the program. While yt-dlp is a command-line program, there are a variety of GUI front-ends for it.
If you can find the link to the actual video file, such as a URL ending with .mp4, .webm, .avi, etc., then you won't need to use yt-dlp since you can just press Ctrl+S if you're watching the video, or right-click the link to save it.
I would also highly recommend re-uploading your saved content to multiple archive websites and other platforms. A good archive service i can recommend for textual content is archive.today. Unlike the Internet Archive, archive.today does not obey web server's robots.txt directives and so anything it is able to access is fair game. Once you archive something with the service, it should be permanent, however given that archive.today is privately owned, there is no guarantee the service won't suddenly disappear. The next best service, and one that works for virtually all content including PDF files and, sometimes, web pages with embedded videos, is archive.org, the Internet Archive. If embedded videos are not playable after archiving a page, one can always use yt-dlp to grab the video and then upload it to the website. If you create an account you can have your own archive library if you wish. Ghostarchive is another resource worth considering.
With regard to accessing content which has been deleted from other platforms, many resources besides the aforementioned are available, including:
- altCensored.com
- Anna's Archive
- Archiveteam
- Avalon Library
- BitChute
- Books Archive - The Unz Review
- Brighteon
- Censored.TV
- FrankSpeech
- Gab TV - Gab Social
- GoyimTV
- Higher Intellect
- Internet Sacred Text Archive
- List of Web archiving initiatives - Wikipedia
- NewTube
- Onevsp
- OurTube
- PDF Archive
- Rumble
- Spotlight News Archive
- The Conspiracy Hole
- The Snowden Archive
- UGETube
- Vid8
- VoluntaryTube
- WHALE
- Youmaker
For more resources, see the Alternative Information Directory and please consider linking to it and submitting more websites.