"If I cherished sin in my heart, the Lord wouldn’t have listened" (66:18). Does that mean God doesn't hear anyone who has sinned?

The verse speaks of the psalmist's own prayer, and it is an if. The next verse answers it: "But most certainly, God has listened. He has heard the voice of my prayer" (66:19). Cherished is ra'ah, the verb of 66:5's see (tap cherished), and the WEB's sin is aven (tap sin). The psalm doesn't say what the psalmist had done, or what was or wasn't held on to. Other Scripture speaks of sin and being heard in more than one way. Isaiah says, "Behold, the LORD’s hand is not shortened, that it can’t save; nor his ear dull, that it can’t hear" (Isaiah 59:1), "But your iniquities have separated you and your God, and your sins have hidden his face from you, so that he will not hear" (Isaiah 59:2). Proverbs says, "He who conceals his sins doesn’t prosper, but whoever confesses and renounces them finds mercy" (Proverbs 28:13). And a psalm says, "I acknowledged my sin to you. I didn’t hide my iniquity" (Psalm 32:5), and "you forgave the iniquity of my sin" (Psalm 32:5). These verses stand side by side in Scripture. These notes don't choose how they fit together, or say more about 66:18 than it says.