I use Fidelity for my brokerage account (not an IRA) but I use Vanguard for my backdoor Roth IRA due to their low fee index funds. My Vanguard account contains a traditional IRA and a Roth IRA.
The traditional IRA is merely a vehicle for getting money into the Roth IRA. I make contributions to the traditional IRA about 4 times a year to hit the $6,000 max. The money never gets invested while in the traditional IRA, where it sits for about 2 days max before doing the backdoor conversion into the Roth IRA.
Once in the Roth IRA, it gets invested into a mix of 3 different funds:
1. Vanguard Total Stock Market Index Fund (VTSAX)
2. Vanguard Total International Stock Index Fund (VTIAX)
3. Vanguard Total Bond Market Index Fund (VBTLX)
These are all index funds which have extremely low fees compared to the mutual funds, individual stocks, or ETFs you would buy through Fidelity. More specifically, these are the Vanguard "Admiral Shares" which are even lower fees than Vanguard's regular index funds, but the Admiral Shares require a specific minimum dollar amount (I think it's $10k?) to qualify, which you wouldn't have starting out, so you would start with the corresponding basic index funds (Investor Shares), which would be VTSMSX, VGTSX, and VBMFX. They will automatically convert to Admiral Shares later on once you have enough money in the Roth IRA.
I know this is all kind of unsolicited advice, but I was at the same point you are a few years ago and I got a lot of different opinions, read several books, and spent time on the Bogleheads forum. It seems like this is the most foolproof approach to retirement planning you can do. You won't get rich by picking a hot stock like Netflix, but you will do very well for yourself over a long period of time. Besides, you can use your Fidelity account for a brokerage account where you play around with GME and other stock gambles.
Also, if anyone else reads this and thinks there is a better way to do it, I'm all ears. This has just been my autopilot approach since making the initial decision to go with it.