Slow JS Loading - causing conversion rate decline since switching to Google Channel/GA4/GTM

[nige123]

Over the summer we switched to Google's GA4 for event tracking. After missing conversion events we switched to the Shopify Google Channel (GA4 + GTM). 

Since this time (late June) we've seen a decline in conversion rates across the board.

A performance analysis of our site suggests slow loading and blocking JS is causing the site to slow down for first-time visitors. Ironically it seems the GA4 javascript loaded via Google Tag Manager is responsible for the bulk of the slow down.

Have others experienced this? Any suggested fixes?

[GadgetBM]

Matic tips: dont use gtag.

[SamuelTBeslogic]

Similarly for us, gtag (Google Tag Manager) is the biggest third party offender in terms of blocking execution (taking about half a second) as reported by PageSpeed.
I downloaded the theme to be sure and there's no reference in code.
We have no Custom Pixels.
We only set it up through the "Google & Youtube" Sales Channel.

It would seem there's not much that can be done other than contacting the app's developers to ask them to load in a non-blocking way.