As you noted, since Vanadium can currently be only updated through an OTA update, you should use a different browser since your Webview is out-of-date (see updated note below). Bromite is a decent choice for an everyday browser, but it sometimes lags behind Chromium during releases. You can also try Mulch, which uses some of Vanadium's patches and gets updated much faster.
Also since Vanadium System Webview is not getting any more updates on your 3a XL, you should go back to using Android System Webview for your main webview provider. Try and install Android System Webview from Aurora Store and then see if Android System Webview is available under 'Settings - Develoepr Options - Webview Implementation'. If it is, then you can use that as your webview provider. I haven't tested to see if this is possible, so hopefully that works for you.
Edit - It looks like the 3a XL received an update on November 28th, so maybe your Vanadium is only lagging behind by about a month?