REST is intended for long-term network-based applications that span several organizations. If you do not see the need for restrictions, do not use them. – Fielding, 2008
Your can Use POST for everything, if you wish. SOAP did that, and more recently GraphQL also leans that way.
But what you abandon are the properties that arise from the most restrictive restrictions of GET. Two of these are that GET requests are secure and cacheable.
Insurance means that general purpose components may know that there is no danger when retrying a batch request; In an unreliable network, they can forward a request autonomously if the response is lost.
Caching, of course, means that we have broadly understood the semantics that not only describe if something can be cached, but for how long and when they should be invalidated.
Essentially, the use of POST for everything reduces HTTP from an application protocol to a transport protocol.