severance and retirement saving

Hi. I was paid severance throughout 2022, but was ineligible for participating in former employer's 401k. I also made some money from self-employment gigs. Say 200,000 gross pay from the former employer, and 20,000 self-employment gross income. I will make a contribution to a solo 401K, but I was planning to calculate that contribution just based on self-employment part of my income. What (if any) retirement vehicle is appropriate for the severance income? I thought I could at least make a $7000 contribution to an old traditional IRA, but Turbotax says I'm ineligible to make a before-tax contribution because my MAGI is too high. Would I be permitted to lump both severance and self-employment income together to calculate a (much higher) contribution limit to the solo 401K?