Here is my current IRA breakdown in a Vanguard fund.
Vanguard Total Bond Index $130,000
Vanguard Intermediate Term $83,000
Vanguard Total International $174,000
Vanguard Target Retirement Income $185,000
Total About $570,000
Vanguard mutual funds can only be bought and sold through Vanguard. So if you move these to Schwab or Fidelity, the trading costs will be very high ($20 per trade or maybe $50 per buy & sell). It's a hassle for Fidelity and Schwab to transact everything through Vanguard.
One way around that is with ETFs. For example, Vanguard Total Bond ETF (BND) and Vanguard Total International ETF (VXUS). I don't think there's a "retirement income" ETF, but maybe you could buy Vanguard Total Stock Market (VTI) instead - with a mix of bonds.
Another way is to sell everything and transfer the cash, then buy funds specific to the broker you use. At Fidelity you'd buy Fidelity mutual funds, etc. If you strongly prefer mutual funds, you might risk holding cash for the duration of the transfer.
I personally prefer ETFs over mutual funds, so that would be my choice in this situation. And actually, our situations have overlap - I've also been a Vanguard customer 20 years, where I've had all my investments until mid 2020. I opened an Interactive Brokers account, then a Schwab account... and now most of my assets are at Schwab. I was so surprised when I called Schwab's customer service line... and they picked up. In general Schwab hold times are very short, and always less than Vanguard's. Same $0/trade for ETFs, too.