The old IDA freeware ver.3.7 supports Z80. It has a Turbo Vision style interface, which may be something that puts you off. It is also no longer distributed officially. However, it is very powerful, and if you can live with its quirks, you will be able to find it on many abandonware websites.
Alternatively, a lot of people started switching to NSA-developed Ghidra: https://ghidra-sre.org/. It is quite powerful, supports Z80, and is also free and open source. The only obvious downside to it is that it is a several hundred Mb download, vs. several megabytes of IDA free 3.7.
Interestingly, 8 years ago a closeely related question was asked over at Reverse Engineering StackExchange: "Is there any disassembler to rival IDA Pro?" Their answers are not specific to Z80, of course, but two interesting disassemblers mentioned there feature support for Z80 and may prove useful too. They are called radare2 and the Online Disassembler.
Over the years, many small(er) disassemblers and disassembling tools have been developed either generally for Z80, or for specific computers based on Z80. A selection of several generic tools for disassembling Z80 code is presented here: http://www.z80.info/z80sdt.htm#SDT_DISASM. In my mind, this selection is very dated, yet, some of the tools there can still be useful.