I was a big fan of early FF run and the '60’s Hanna-Barbera animated version. Doctor Doom is sorely missed in the MCU. Fans actually wanted to see him cross paths with Vader back in the day.
Reed Richards had enough dangerous experiments going on they could have all been trapped in another dimension where time flows differently or something. The Baxter Building could be this mysterious edifice that’s been sealed off for decades, when weird things begin to happen. I’d be up for a FF movie set in the early 60’s before bringing them forward to the current time.