Or if you can't upload because you live in Siberia or the Rural parts of the UK, and you have an SD card in your Switch:
Save Replay
Go into Replays, find the recording
Convert to Video (figure out how the recording feature works, it's not the most intuitive)
Once converted, properly power off Switch (don't just press the button but hold it, bring up the menu, choose power off)
Extract SD card
Use a micro-SD card reader and dump it out onto either PC or whatever device you have
Find the video recording (the SD isn't well organised so you'll have to do a file search probably)
Either upload it to a third party video hosting site, OR convert the video to be under 8mb or 20mb (whichever is your Discord limit)
Link/Upload here
(Be sure to reinsert the SD card into the Switch before powering it back on, and make sure it recognises the card. If it doesn't, repeat removal and insertion, powering off properly each time. A pain, but I didn't invent the damn thing.)