Transferring 401ks or SEP/Simple IRAs from old employers

I left one employer in 2021 where I had a SEP/Simple IRA, but now I can't contribute to it. Can I convert that balance into a Roth IRA to continue contributing and adding to that amount on my own? What are the tax implications? I read that if I wait two years after the end of my employment with this company to convert the account, or transfer the entire balance from a SEP into a Roth account (thereby closing the SEP/Simple IRA account), I won't have to pay taxes on it, is this correct?

 

Also this year 2022, I left my most recent full-time employer to work as an independent contractor, what should I do with my retirement account (401k) from them?