I have seen that SSD storage needs electricity, in order to not lose data, so:
If a Linux system with an UPS, that works as a NAS that runs 24/7 existed, and the data would be only written 1-10 times, the "full" capacity of the each physical drive, so TBW wouldn't be an issue, with, a Raid 1 consisting of 4 drives used for 4k videos, and after a few years for 8k videos, would It be better to use SSDs or HDDs for this purpose with unlimited money and wanting a "no need to modify me for an eternity system"?
With equal parts, would the HDDs system be more or less reliable than the SSDs system?
If you have money for an SSD system, then why not? Also, there is no "no need to modify me for an eternity system" as such. Backups and periodic verification is a must if you want to keep your data. No matter HDDs or SSDs. Also, RAID 1 with 4 SSDs? That's only 1 SSD usable capacity. Unless you mean RAIDZ1.