I've been working with and enjoying technology most of my life. As such (and given the long history of vendor lock-in and associated cost/challenge with going without the support of major tech companies), I have a pretty significant footprint with certain tech companies. I've been with Google/Gmail/Android for many years. I have files stored up on Onedrive and Google Cloud. I have been working with Windows, ChromeOS, and even macOS and iOS at various stages as long as I have been working with computers. After some self-education I've come to the conclusion that these dependencies must end and have been on a path to rid myself of external influences.
This is an ongoing list of issues I've come across and alternatives found. This is by no means a comprehensive list; this is more just a few examples of alternatives I've been able to fill the holes with.
It's an unfortunate reality that communication platforms are among the hardest things to abandon. After all, your friends and family have probably come to depend on them despite telling you years ago that such channels of communication were "not as good as a phone call". Facebook, Twitter, and others know this all too well, and try to buy up the landscape around them in order to ensure that you can't go too far outside of their sphere of influence even if you "cancel" your main account.
I've cancelled Facebook at least twice at this point. The first time was a few years back after a mental break that saw me re-evaluating how I interacted with the internet in general. More recently, though, I simply decided to leave. I don't like Facebook as a company or as a product, so it seemed silly to stick around using it. Twitter was a little harder to give up on, but eventually I moved away in favour of my own Mastodon server.
For chat, Matrix seems to be the ideal candidate to take over from proprietary solutions. I tend to use this with Weechat, but the more glossy clients such as Riot and Fractal are also available for people not so inclined to use a terminal application.
Productivity is generally less of an issue in my experience, as productivity tools are almost invariably superior in the free software world and it is not a requirement that everybody use the same monolithic tools in order to work with each other in every case. I personally can get most of what I need to do done with Vim, Pandoc, LaTeX, and git.
The area with which I do struggle sometimes is audio/video production. While there are some excellent tools for these, I have come across quite a few issues with hooking equipment up to a GNU/Linux powered machine and not having access to its full range of features. It's a shame, as it's not the fault of the software developers as much as the OEMs. Most things are designed explicitly for Windows or macOS in these fields, but it is encouraging to see so much work going in to it on the GNU/Linux and *BSD worlds.
Gaming on Linux has improved significantly with the release of Steam's Proton. However, while this is an impressive piece of technology, it is nonetheless keeping you locked in to a specific company and denying you the freedom to do with your games as you will. Luckily, I don't play games on my computer much.
I've been able to replace Soundcloud/Spotify/Google Play Music with Funkwhale and have enjoyed being able to run this with the mopidy-subidy plugin on my machine.