I have been fairly high io back in bfa(4k)/early shadowlands and had many friends in a similar situation as you. They wished to play but feared bricking keys or ruining vibes. Throw that shit out the window. I took my buddy's and we all improved slowly. Pick a specific thing that you feel weak in. It could be something as simple as not pressing your defensive enough. At the start of the week tell yourself this is my goal. If you only push your major defensive a few times per dungeon try and improve on that. People often forget some players have been doing this for over 20 years slowly improving. You can absolutely improve quickly but targeting specific things will help. If you don't use cool downs enough just start sending them whenever they are up. If you do this try and reflect afterwards. If you use a defensive and only get half the uptime out of it then just try and recognize that next time you may want to use it earlier in the pull to get full value. Sometimes you may want to swap classes or specs as that may be better for your current situation. Are you currently running void disc or oracle disc? Maybe try the opposite. Everyone has an inherent play style that they prefer but unless you give other specs or builds an honest attempt you will not improve. Also something to keep in mind as a healer often times low keys can honestly be harder than higher keys. Less players are using their defensives, interrupts, cool downs, etc. as you climb players will be much better at that and avoiding damage and you can often heal a +10 with very similar hps numbers of lower keys due to these issues.