This post feels incomplete. What alternatives to F-Droid should we be considering?

Planning to sell in taxable this year to raise cash so I can max out traditional 401k. Will be all long term capital gain and my calculations have me wringing out a few extra thousand in tax savings. Trick is going to be selling and buying (similar but different indices) at the same time to stay in the market since workplace doesn’t always buy precisely on payday and taxable holdings are all ETFs (versus mutual funds in 401k). More trouble than it’s worth? Wish I made enough to max out without selling, but that’s a topic for another day.