iPhone XS Max question battery replacement

Yes. In addition you'll lose the ability to view your battery health information.

Outside of paying Apple to replace your battery, the only way around this issue is to save the BMS, or Battery Management System, from the old battery and transplant it to a replacement battery cell. It also takes several tools that most of us don't have lying around including a spot welder and a device programmer. I have the tools to do this myself, and I figure I've got about $150 into the necessary tools and supplies.

So it's a judgement call for you; do you want to make that much of an investment in tools you may only use once, live with the warning message, or pay Apple?

It also occurred to me that you may be able to locate a repair shop that is capable of doing a BMS swap and being able to reprogram the battery health statistics (cycle count and percentage), so that could be another option.