There is, generally, no direct legal requirement as such. Organisations choose whether or not to implement the requirements of ISO 27001 based upon the benefits that would be gained by doing so.
However, you should pay close attention to any contractual obligations you may have for protecting the information of clients and other stakeholders.
There is an increasing trend where customers require third party suppliers to implement or certify to ISO 27001, thus making it a legal requirement, by way of a contract.

ISO 27001 Clause 7.5: Documented Information Explained
URM’s blog breaks down ISO 27001 Clause 7.5 requirements, with practical guidance on how to achieve conformance to this Clause & what external assessors expect.
URM’s blog explains the purpose & requirements of ISO 27001 Clause 6.3, types of ISMS change it covers, and key considerations when putting it into practice.
If your organisation is looking to transition to ISO 27001:2022, URM’s blog provides practical and invaluable guidance on meeting the new requirements.
URM’s blog explains how the principles of confidentiality, integrity and availability (CIA) can help align your information security controls with best practice

