I would recommend pika for easy backup, steamdeck (or even a windows pc) could have problems with cloud saves. If you want real backups you should set up deduplicated archives. This means you just install pika and click a couple times. You can set it to backup over ssh. The deduplicated compressed backup is often smaller than source data size even if it has years of archives.

It’s commonly called coil whine. You might want to tweak BIOS and try to disable C-states or such power saving features of the processor. The main problem is a physical problem in your motherboard. Having linux can change the sound but won’t fix this issue. Only real fix I see is to get a new mb eventually. But if Linux reduces it, go for it!

https://randompctips.blogspot.com/2021/04/how-to-get-rid-of-coil-whine-by.html

https://en.wikipedia.org/wiki/Electromagnetically_induced_acoustic_noise

I can recommend duplicati on windows or pika backup (which is a borg backup gui) on linux. Then just make a user on raspberry pi and enter the ssh login in your backup client and you’re set.

Duplicati / Pika / Borg will encrypt the backups for you! So there is no danger of someone reading or changing your backups. You could use even some free cloud storage to store the backups safely. It really doesn’t matter where you store them.

Rsync won’t deduplicate or make archives so you cannot restore a backup from any chosen date. Rsync is sync not backup.