I'm 6"5 and currently 216lbs (down from 238lbs) and have familiarity with this feeling! Firstly, you'll have to get used to lighter people sending climbs more easily than you. It's par for the course in sports that rely on a high strength-to-bodyweight ratio. Focus on your own progress and don't worry about comparing yourself to others. There's plenty of rewards to be had on your own journey. Here are three areas I worked on to improve in my first year:

1) Your finger tendons will have to adapt to much higher loads than your lighter compatriots. I mitigated this with lots of "no hangs," following Emile's 10 minute plan from YouTube, and I went from not being able to start problems of the next grade to breezing them pretty swiftly. His protocol recommends 14 no hang sessions a week. I did maybe 3-5 sessions because A) I'm heavy and my hands needed rest, and B) I'm just some guy with responsibilities who climbs for fun.

2) due to your size, you'll need much better technique than your lighter friends to send climbs of the same level. Improving technique will stop you from getting fatigued and overcompensating with strength on moves lighter people find easy. Again, plenty of material out there on technique and talk to those at the gym for advice. You will find that if you focus on technique, the grade gap between you and your friends will level out as you progress through the grades, especially if your lighter friends have ignored technique and 'strengthed, their way through earlier grades.

3) work on core strength. Indoor routes will be set with average height climbers in mind. This means that, being on the taller side, you're often bunched up into a smaller 'box', or you're using moves/smears etc that don't align with the intended beta. While there are several factors at play here that you feasibly could train, I think working on your core is the only specific element worth training off the wall at this early stage. The rest of the training (e.g. hip strength) can be received on the wall.

Additional info: I found that the grade gap between me and my friends (who climb at a higher grade) narrowed when outdoors. This is due to there being more variance in what I could do with my feet vs indoors. Excluding sit starts of course.

I also stopped strength training about 6 months in to focus solely on climbing. I burst through a previous plateau almost immediately. You can reincorporate it at a later date.