SeedCracker VS MCeed-A

If you don't respect this, you can use https://github.com/KaptainWutax/SeedCracker

Custom code, usually. KaptainWutax made a program a few years ago which can crack seeds just by scanning the world. When seed cracking, though, you are looking for certain features which can rule out many many seeds very easily. For example, finding specific dungeon coordinates and mossy cobble patterns can narrow it down dramatically. For this process, you need not scan that much since it's some simple maths applied to not that many blocks and not checking very many times.

Im not an expert but cords are needed or at least if you want to solve it in any time. you say you play on that SMP so maybe use seedcrackermod but KaptainWutax. It is a fabric mod that searches the world for structures like shipwrecks and once you find 5 of them it can crack the seed within minutes or even less (depends on your gpu)

Otherwise, I found a mod that will calculate a server's seed but you have to actually be on the server; most of the actual tools seem to be private, most likely due to security concerns as stated above.

Of course, finding the seed used to generate a world, or part of a world, is a completely different matter, requiring a special program which uses GPU computing on a higher-end GPU to brute-force the seed (this is actually possible, or was until they changed world generation in 1.18 to entirely use the full 64 bit seed; previously, only the biome map was fully 64 bit and everything else used Java's "Random", which only uses 48 bits, which is a factor of 65536 times less - as noted here, a 2 hour search would now take 14 years, likewise, "Minecraft at Home" uses large-scale distributed computing and special hardware to find the seeds for things like the panorama, and can still take months).

https://gitlab.com/taleden/MCeed-A (note that this will not work in the latest versions)