startup screen freezes

I have a 6 yo iMac, has been slowing down, in part due to decreasing available RAM and near maxed out storage. It froze while working on a project, turned off, but would not fully reboot after I turned it back on. It would get to the loading “bar” showing it was done, but wouldn’t move past the Apple screen. I’ve tried, and been unable, to get to safe mode. Was able to run first aid on the disk, but everything checked out. I haven’t backed it up in several months...ugh.