Thanks for the link that explains WHY we are all having such issues getting CarPlay to work properly as it should.
If it works on the cars I would think it’s not an iPhone issue, rather an issue with the GTS boom system.
Just my 2c

I feel it is a Harley issue like you.
My iPhone 11 works great in my 2017 F-150. No CarPlay issues at all, connected every time the first time. My truck has never had to have software updated.
My iPhone 11 works great in my 2018 Corvette. No CarPlay issues at all. connects first time every time. Have never updated the car software.
My iPhone 11 works great with my Sena 20S, HD brand if not paired to bike. Volume on music so loud you never go over half. Phone calls crystal clear.
Problem is when iPhone 11 is pair to bike and phone is. No phone call possible. music volume low.
Kicker is, yesterday for example, everything paired and worked including CarPlay came up first time I start the bike. All I do is shut bike off for gas, restart the bike. CarPlay does not come up. Have to kill bike for a minute, and restart. CarPlay comes up. Hit or miss all day weather or not CarPlay would come up when restarting bike.
Harley just doesn't care. More concerned about getting the google version of CarPlay released. Sort of like failing lifter in the 110 bikes, never did fix it after 10 years.