honestly after years of shooting weddings the Godox V1-C TTL Round Head Flash is basically unmatched. it recycles way faster than your old generic gear and that lithium battery lasts all day. if you prefer sticking to native stuff, the Canon Speedlite 430EX III-RT is super reliable with the 90D metering but it definitely feels underpowered compared to the Godox. id grab the V1 tho.

Late to the thread but you really gotta be careful with gear on a budget... if that AF beam is glitching, it might be a communication error with your shoe pins or outdated firmware. I would suggest looking at these:

• Godox V860III-C TTL Li-ion Flash is probably your safest bet. It has a lithium battery which is a total lifesaver for weddings. You wont be fumbling with AAs during the vows and the recycle speed is consistent.
• Godox TT685II-C TTL Flash is a solid cheaper alternative. Just be careful cuz the recycle time gets sluggish once the batteries hit 50 percent.
• Yongnuo YN600EX-RT II TTL Speedlite is a decent clone of the high-end Canon stuff. It plays nice with the RT system but honestly the build feels a bit plastic-y. Whatever you get, make sure to test it thoroughly before the Philly trip. The 90D has some weird timing quirks.

honestly be careful with jumping into new gear right before a big wedding like that. i might want to consider just renting something higher end if you are worried about reliability on a budget because weddings are such high stakes. speaking of philly though... if you are shooting downtown make sure to watch your gear. i was there for a gig last summer and got so distracted by this street performer near city hall that i almost left my bag on a bench. then i ended up wandering into a cheesesteak spot and spent like forty minutes debating with a local about which place is actually the best. turns out everyone has a different opinion and they are all very loud about it lol. the grilled onions were killer though. anyway sorry kinda went off topic there... just thinking about those steaks now.