rpc, mempool: rpcdeprecate `fullrbf` key in getmempoolinfo RPC response

diff --git a/src/rpc/mempool.cpp b/src/rpc/mempool.cpp
index 1a94d10b..1b76f7d8 100644
--- a/src/rpc/mempool.cpp
+++ b/src/rpc/mempool.cpp
@@ -1055,12 +1055,14 @@ UniValue MempoolInfoToJSON(const CTxMemPool& pool)
     ret.pushKV("minrelaytxfee", ValueFromAmount(pool.m_opts.min_relay_feerate.GetFeePerK()));
     ret.pushKV("incrementalrelayfee", ValueFromAmount(pool.m_opts.incremental_relay_feerate.GetFeePerK()));
     ret.pushKV("unbroadcastcount", pool.GetUnbroadcastTxs().size());
-    ret.pushKV("fullrbf", true);
     ret.pushKV("permitbaremultisig", pool.m_opts.permit_bare_multisig);
     ret.pushKV("maxdatacarriersize", pool.m_opts.max_datacarrier_bytes.value_or(0));
     ret.pushKV("limitclustercount", pool.m_opts.limits.cluster_count);
     ret.pushKV("limitclustersize", pool.m_opts.limits.cluster_size_vbytes);
     ret.pushKV("optimal", pool.m_txgraph->DoWork(0)); // 0 work is a quick check for known optimality
+    if (IsDeprecatedRPCEnabled("fullrbf")) {
+        ret.pushKV("fullrbf", true);
+    }
     return ret;
 }
 
@@ -1071,24 +1073,30 @@ static RPCHelpMan getmempoolinfo()
         {},
         RPCResult{
             RPCResult::Type::OBJ, "", "",
-            {
-                {RPCResult::Type::BOOL, "loaded", "True if the initial load attempt of the persisted mempool finished"},
-                {RPCResult::Type::NUM, "size", "Current tx count"},
-                {RPCResult::Type::NUM, "bytes", "Sum of all virtual transaction sizes as defined in BIP 141. Differs from actual serialized size because witness data is discounted"},
-                {RPCResult::Type::NUM, "usage", "Total memory usage for the mempool"},
-                {RPCResult::Type::STR_AMOUNT, "total_fee", "Total fees for the mempool in " + CURRENCY_UNIT + ", ignoring modified fees through prioritisetransaction"},
-                {RPCResult::Type::NUM, "maxmempool", "Maximum memory usage for the mempool"},
-                {RPCResult::Type::STR_AMOUNT, "mempoolminfee", "Minimum fee rate in " + CURRENCY_UNIT + "/kvB for tx to be accepted. Is the maximum of minrelaytxfee and minimum mempool fee"},
-                {RPCResult::Type::STR_AMOUNT, "minrelaytxfee", "Current minimum relay fee for transactions"},
-                {RPCResult::Type::NUM, "incrementalrelayfee", "minimum fee rate increment for mempool limiting or replacement in " + CURRENCY_UNIT + "/kvB"},
-                {RPCResult::Type::NUM, "unbroadcastcount", "Current number of transactions that haven't passed initial broadcast yet"},
-                {RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection (DEPRECATED)"},
-                {RPCResult::Type::BOOL, "permitbaremultisig", "True if the mempool accepts transactions with bare multisig outputs"},
-                {RPCResult::Type::NUM, "maxdatacarriersize", "Maximum number of bytes that can be used by OP_RETURN outputs in the mempool"},
-                {RPCResult::Type::NUM, "limitclustercount", "Maximum number of transactions that can be in a cluster (configured by -limitclustercount)"},
-                {RPCResult::Type::NUM, "limitclustersize", "Maximum size of a cluster in virtual bytes (configured by -limitclustersize)"},
-                {RPCResult::Type::BOOL, "optimal", "If the mempool is in a known-optimal transaction ordering"},
-            }},
+            [](){
+                std::vector<RPCResult> list = {
+                    {RPCResult::Type::BOOL, "loaded", "True if the initial load attempt of the persisted mempool finished"},
+                    {RPCResult::Type::NUM, "size", "Current tx count"},
+                    {RPCResult::Type::NUM, "bytes", "Sum of all virtual transaction sizes as defined in BIP 141. Differs from actual serialized size because witness data is discounted"},
+                    {RPCResult::Type::NUM, "usage", "Total memory usage for the mempool"},
+                    {RPCResult::Type::STR_AMOUNT, "total_fee", "Total fees for the mempool in " + CURRENCY_UNIT + ", ignoring modified fees through prioritisetransaction"},
+                    {RPCResult::Type::NUM, "maxmempool", "Maximum memory usage for the mempool"},
+                    {RPCResult::Type::STR_AMOUNT, "mempoolminfee", "Minimum fee rate in " + CURRENCY_UNIT + "/kvB for tx to be accepted. Is the maximum of minrelaytxfee and minimum mempool fee"},
+                    {RPCResult::Type::STR_AMOUNT, "minrelaytxfee", "Current minimum relay fee for transactions"},
+                    {RPCResult::Type::NUM, "incrementalrelayfee", "minimum fee rate increment for mempool limiting or replacement in " + CURRENCY_UNIT + "/kvB"},
+                    {RPCResult::Type::NUM, "unbroadcastcount", "Current number of transactions that haven't passed initial broadcast yet"},
+                    {RPCResult::Type::BOOL, "permitbaremultisig", "True if the mempool accepts transactions with bare multisig outputs"},
+                    {RPCResult::Type::NUM, "maxdatacarriersize", "Maximum number of bytes that can be used by OP_RETURN outputs in the mempool"},
+                    {RPCResult::Type::NUM, "limitclustercount", "Maximum number of transactions that can be in a cluster (configured by -limitclustercount)"},
+                    {RPCResult::Type::NUM, "limitclustersize", "Maximum size of a cluster in virtual bytes (configured by -limitclustersize)"},
+                    {RPCResult::Type::BOOL, "optimal", "If the mempool is in a known-optimal transaction ordering"},
+                };
+                if (IsDeprecatedRPCEnabled("fullrbf")) {
+                    list.emplace_back(RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection (DEPRECATED)");
+                }
+                return list;
+            }()
+            },
         RPCExamples{
             HelpExampleCli("getmempoolinfo", "")
             + HelpExampleRpc("getmempoolinfo", "")
diff --git a/test/functional/feature_rbf.py b/test/functional/feature_rbf.py
index a2c8cb60..5527f7a9 100755
--- a/test/functional/feature_rbf.py
+++ b/test/functional/feature_rbf.py
@@ -28,6 +28,7 @@ class ReplaceByFeeTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 2
         self.uses_wallet = None
+        self.extra_args = [["-deprecatedrpc=fullrbf"], []]
 
     def run_test(self):
         self.wallet = MiniWallet(self.nodes[0])