I've got some steps to provide, @info-allaboutout.
In QuickBooks Online (QBO), you can reactivate inactive accounts by following these steps:
1. On the upper right corner, look for Settings then select Chart of accounts.
2. Select the Gear icon next to the printer icon. Then select Include inactive.
3. Find the account you want to use again, then select Make active.
To keep everything accurate, you'll still see inactive accounts and their transactions when you run reports in QuickBooks Online (QBO). Upon doing so, you can now make some of your accounts active again.
Lastly, I've added a resource that you can browse through for you to be able to keep your Chart of accounts organized when adding an account: Add an account to a COA in QuickBooks Online.
If you still need assistance managing inactive accounts or anything else about QuickBooks, please know that I'm just one post away. Stay safe and have a good one.