Honestly, the easiest way I manage it is just using whatever tools each platform already gives you. Instagram and Facebook are the simplest because Meta Business Suite handles both at the same time, you can schedule posts, reels, check messages, all in one place. Saves a ton of switching back and forth.
TikTok has a web scheduler, YouTube lets you schedule inside Studio, Pinterest has one, and even LinkedIn finally added scheduling. None of them are perfect, but they do enough if you’re just trying to stay consistent without downloading five different apps.
I used to manually post on everything and it was a nightmare. What actually helped was batch-creating stuff once or twice a week, then using the native schedulers to line everything up. Takes way less mental energy and makes staying consistent way easier.