Yeah it doesn't seem a method was included to get the pointer that you need, leaving only options not worth the trouble. Might want to use the twinBASIC WebView2 control; if you're not ready to switch to tB I've wrapped it in an ActiveX control that works in VB6/VBA/etc. It comes with an event to receive the results of the call you're looking for by default with no need for modification. Switching to that will be easier than trying to dig out the pointer.

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If you're looking for an alternative, there's always twinBasic. It comes with an open source(-ish?) WebView2 implementation on top of a closed-source language/compiler that's mostly VB6 compatible. It's getting more compatible by the day and it only costs $35 USD/month, forever. Sure, it’s also a one-man show, but the "one man" is still really active compared to the other "one man", and this time it's different...If either you or he runs out of money, the whole thing just stops working completely
Maybe I missed the sarcasm but the idea either your code or the tB IDE/compiler just 'stops working completely' because either side runs out of money is absurdly false. There's a free community edition where the only limitation is a splash screen on x64 binaries, and no LLVM optimization (barely any of it implemented yet). As the "free" suggests, this costs $0 per month, not $35 per month. If you do get a premium subscription then stop paying, it just reverts to the community edition. Nothing stops working. And your binaries stay as is, there's no license checks in your code; an exe built with an active subscription will remain splashscreen free forever. If Wayne runs out of money, worst case is tB stays as it is now, already far ahead of VB6 in features and complete enough you can work around bugs and unimplemented parts. And that's if it happens soon before tB leaves Beta. Once it hits v1.0 the source goes into escrow to be released if abandoned.