It's not Archer C5 I think, it's specially manufactured by TurkTelekom. According to this forum post, second guy there say TP-LINK gave him the GPL source code in that link. He reviewed it some and said it's probably a Mediatek EN7512 CPU: https://forum.donanimhaber.com/turktelekom-tplink-c5v-fiber-modem-kullananlar--135151256-11
This is the GPL source code of it: https://static.tp-link.com/upload/gpl-code/2022/202209/20220902/ArcherC5v_GPL.tar.gz
Btw here is the teardown of it: https://forum.donanimhaber.com/tp-link-archer-c5v-teardown-ici-merak-edenlere--152255431
The CPU plate can't be removed easily. He says it's sealed shut, if he had removed he probably can't put it back. Is the situation hopeless totally?