I have created a Solr version 8.1.1 in Azure using a Docker for Sitecore. I get the following error for a large query:
ERROR Error during executing a query.
Exception: SolrNet.Exceptions.SolrConnectionException
Message: <h1>Bad Message 431</h1><pre>reason: Request Header Fields Too Large</pre>
Source: SolrNet
at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable`1 parameters)
at SolrNet.Impl.SolrQueryExecuter`1.Execute(ISolrQuery q, QueryOptions options)
at Sitecore.ContentSearch.SolrProvider.LinqToSolrIndex`1.ExecuteQuery(SolrCompositeQuery compositeQuery, QueryOptions options)
Nested Exception
Exception: System.Net.WebException
Message: The remote server returned an error: (431) Request Header Fields Too Large.
Source: System
at System.Net.HttpWebRequest.GetResponse()
at HttpWebAdapters.Adapters.HttpWebRequestAdapter.GetResponse()
at SolrNet.Impl.SolrConnection.GetResponse(IHttpWebRequest request)
at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable`1 parameters)