Yes, IP cores are very expensive to license, if they’re even available for licensing at all. This is part of the appeal of RISC-V - an open-spec, royalty-free processor architecture that is free of charge for chip designers to implement.
Any implementation of it has the exact same patent minefield to navigate as any other ISA. Most of the patents are around implementation techniques not instruction set.
https://riscv.org/technical/specifications/risc-v-genealogy/
Of course, the various extensions might violate current patents (I would guess that packed SIMD and cryptography extensions are particularly at risk). But the basic ISA does not use anything that was not already widely adopted by 2003.
Besides that, engineers in large companies are told to explicitly not look up any patents so they won't be accused of willful infringement.