GXExplorer

You could build a low power repeater. Problem will be you will need an indoor and outdoor antenna. When the repeater transmitting. You will lose half of the power to each antenna. Plus a mess of other things that could go wrong.

I had looked at passive repeaters/antennas. But the usefulness of them are low. In your case. I would investigate this an option. Don't expect much, but to spend money. You could try to build a dipole indoors connected to a yagi outside pointed at the area of intrest. But again passive repeaters aren't in high use for a reason.

Another option is to get a kg100g, or any radio with a Bluetooth option. With a Bluetooth mic and connect the kg to an external antenna.

For hams, I have contemplated buy a uv578 with Bluetooth head control mic. But always just walk over to one of my digital radios and use the hotspot. Haven't seen a gmrs (tuned) hotspot yet. Guess that will be on a to do list.

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If you have a strong signal outside those metal walls - a passive repeater (just 2 antennas hooked together as described above by kidphc) is a workable solution. I usually tell people that a passive antenna system will fix a small problem in a small area.
You use an outdoor Yagi directional antenna pointed towards the repeater site, along with LOW loss (Heliax hardline is your friend for this type of setup) cable with the fewest possible connectors. Any loss is more loss than you want. Then install and connect an interior antenna in the center of the room/area where you need signal the most.  The antenna system acts as a conduit/pipeline for the signal - both incoming and outgoing... thus the passive repeater nickname. Plus, that sounds more exotic than "I'm gonna screw 2 antennas together back to back".
I've done setups like this for job trailers or basement offices, and while I tell the customer they can expect portable coverage within 8-10 feet of the interior antenna, they usually do better than double that. You should have an outdoor signal level above -85 dBm for this type of setup to work. Stronger levels are better, but if the signal level was that strong outside, you probably wouldn't be having the issue inside.
 

I’ll second getting to understand repeater programming.  Go to the Mygmrs map and look for repeaters in your area. I would download Chirp for programming. That radio comes with a lot of preprogrammed scanner frequencies.  Me personally, I would investigate which ones are really relevant to my area and note ones I might get rid of. When you get it, down load a back up untouched. I tend to do that every time I make changes in case I mess something up.  Here are some tools that may help along the way.  Looks like you chose a good radio enjoy.  Chirp  Radio Reference  Line of Site Tool

In addition to what Lscott presented, remember that a GMRS license enables you to talk like a normal person on a normal radio. No CB jargon, no fancy ham radio lingo, no codes, nothing. ID when you're supposed to, be polite, wait your turn, that kind of thing. Talk to people like you would talk on the phone or in person. Don't overthink it. There are endless threads here where people fall down rabbit holes overanalyzing no end of minutia. 

I would HIGHLY recommend you read over the GMRS service rules. It will save you asking some questions later on.
https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-E
Getting familiar with the channel frequencies/channel numbers/power level allowed helps when reading various posts.
https://en.wikipedia.org/wiki/General_Mobile_Radio_Service
Finally getting the hang of how the whole repeater thing works helps a lot when trying to figure out how to program your radio. This topic seems to trip up a lot of first time users.
https://woofthebeatenpath.com/how-do-you-use-a-gmrs-repeater-for-longer-range/
https://www.youtube.com/watch?v=kxbL2g4E7KU
If you have any more questions we're all right here. ?

https://www.aljazeera.com/economy/2022/11/25/us-bans-chinese-telecom-devices-citing-national-security

I've wondered myself if some two-way radio companies from overseas have placed a possible sabotage chip in said radios (including military radios) that would "brick" the radio either after receiving a series of predetermined tones or data. That way, if an offending country with that knowledge wanted to declare war with us, they could shutdown all of the compromised radios to cripple communications. 
Maybe I'm just paranoid, lol.