Yeah use your iMac. Use a VPN. Top VPNs all should work on your iMac. Proton and Mullvad are the top recommended.

Transmission is the client I use. It’s great.

You’ll need to find more sites. Pirate Bay is huge, and 1337x is big. Private trackers are the best. You’ll need to wait for an open signup or interview to get started. You’ll need to watch the opensignups subreddit on the R*dot site for signups, unfortunately. Ignore all of these unhelpful bitches who tell you you can’t do it with what you have. You’ll just want to use your iMac for easiest downloading.

First, you buy an eye patch. And maybe some small and energy efficient computer. A Raspberry Pi 5 might even be enough for your first steps. Or maybe some small form-factor PC. Then you install Linux on there and follow one of the various guides for Linux.

I’m really exhausted

We all are!

How would you do it on any other device? The same way.

Docker and docker compose should work within macos, or not? (its a unix after all) you could setup a test environment there (jellyfin, navidrome, nextcloud and the like). I'm not sure which iMac... they use arm and RISC processors in some of them I heard. It is possible you won't find docker-images which are made for these processors. Amd64 (Intel, amd) is the least problematic in this regard.

For always on services (like filesharing or nas) a low power device would be good (a used raspberry. or celeron n powered all-in-one device if you want to have an UEFI capable and amd64 compatible platform with sata, more LAN ports and m.2.)

VPN and maybe a parrot are recommended too. ;)

Edit:
For streaming maybe a VPN / anonymizing proxy is sufficient. In some countries even this shouldn't be necessary but it doesn't hurt. If you pay for illegal streaming they might catch you via the money trail when the platform is seized. But i doubt it that they care about the customers, they should just be after the providing party.

Not so fast sailor! Do this first

✔️ Recommended: Use Firefox + uBlock Origin.
    Firefox is the top non-Chromium browser, offering nice security and privacy features. It also boasts the best compatibility with uBlock Origin for effectively blocking ads and other harmful web content.
✔️ Recommended: Change your DNS settings.
    DNS can enhance the browsing experience by increasing speed and bypassing restrictions, as your Internet Service Provider (ISP) usually offers a slower default DNS that may censor websites according to their preferences.
🧲 For torrenting: Install a reputable torrent client such as qBittorrent.
    Torrent client is a separate program that is essential for downloading files via torrent files, which is a method distinct from direct downloads.
🧲 For torrenting: Set up a VPN network such as AirVPN or ProtonVPN.
    VPN enhances online privacy and security by encrypting the connection and masking the IP address, making it ideal for torrenting as it protects your identity, and allows access to restricted content.
🧲 For torrenting: Bind the torrent client to the VPN interface.
    Ensures torrenting only happen when the VPN is active, lowering the chances of a leak of the IP address to essentially zero.

Not sure what the best solution for sports is, but the simplest, most reliable option for streaming is a debrid subscription used in conjunction with Stremio on MacOS, Vidi on Apple TV, and Stremio Lite or Vidi on iOS.

While there's free websites that aggregate streaming servers for movies and tv shows, their unreliability arguably makes debrid reliability worth the added cost. Here's a debrid service pricing chart.

The biggest ability for to do anything about system is MacOS only everything else so much locked down