Homepage layout shifts - degrading SEO / page speed

Hi, we run 4.3.6 (dated but a lot of customizations and integrations so not ready to upgrade yet). We have a couple layout shifts on page load that are negatively effecting our page speed scoring for SEO so I am trying to fix them. In layouts, we have a grid setup with a width of 16 and content alignment at “full width” and an offset of 0. No user-defied css-class. Inside each grid (I have tested with each banner in its own grid and with them all in one grid), we have a block(s), each of which is a banner block with a template of “original” and linked to a banner. They all display properly but when I run the website through some performance analysis tools, they are showing layout shifts because (per test site) they lack a definied aspect ratio. Any one have an easy way for me to fix this?