You need to join the clan with your PSN account, not your Steam account, as PSN is where your character data actually resides. Cross-save is allowing you to use your PSN save data on Steam, but that data will always be permanently tied to your PSN account, and nothing transfers between accounts. Your Steam account data is dormant, due to cross-save overriding its data, which is why it shows as inactive. Join the clan with your PSN account, then have your Steam account pass on the founder status to the PSN account, and leave the clan from the Steam account. Only the active account needs to be in the clan, and whichever platform you play on, you will have access to the clan benefits.