[SalesForce] Popping up a modal on a LWC makes contents scroll to top

This is a part of the HTML of my LWC:

<template>
  <div class="slds-grid slds-grid_vertical">
    ...
    <lightning-datatable ...>
    ...
  </div>
  <template if:true={openBackOrdersModal}>
    <section role="dialog" tabindex="-1" class="slds-modal slds-fade-in-open slds-modal_medium" aria-labelledby="modal-heading-bo" aria-modal="true" aria-describedby="modal-content-id-bo">
      <div class="slds-modal__container">
        <header class="slds-modal__header">
          <button class="slds-button slds-button_icon slds-modal__close slds-button_icon-inverse" title={label.ditVensterSluiten} onclick={closeBackOrdersModal}>
            <lightning-icon icon-name="utility:close" variant="inverse" size="small"></lightning-icon>
          </button>
          <h3 id="modal-heading-bo" class="slds-modal__title slds-hyphenate">{backOrdersModalTitle}</h3>
        </header>
        <div class="slds-modal__content slds-p-around_medium" id="modal-content-id-bo">
          <lightning-datatable
            key-field="Id"
            data={backOrders}
            columns={backOrderColumns}
            is-loading={isLoading}
            hide-checkbox-column="true"
            suppress-bottom-bar="true">
          </lightning-datatable>
        </div>
      </div>
    </section>
    <div class="slds-backdrop slds-backdrop_open"></div>
  </template>
</template>

openBackOrdersModal is set to true when some button on the LWC is clicked. The modal is displayed, but the contents of the LWC, on top of which the modal is displayed, are scrolled all the way to the top.

The contents of the LWC, which itself is a modal window, are longer then the screen, so scrolling is necessary to see the bottom part. The LWC contains, amongst other things, a datatable where each row has a button.
The contents of the modal are dependent on the button that is clicked. The users sometimes need to click several buttons to inspect details for each of the rows.

As it is now, the user scrolls down, clicks a button, modal is displayed, and the contents of the LWC are scrolled all the way to the top (this is instantaneous). So the user must scroll down once more, click another button, and so on and so on.
This is very annoying for the user. I found the HTML code for the modal for the most part of it on the internets, the modal part I found here.

Some more googling let me to this general solution. It proposes:

When the modal is shown:

document.body.style.position = 'fixed';
document.body.style.top = `-${window.scrollY}px`;

When the modal is hidden:

const scrollY = document.body.style.top;
document.body.style.position = '';
document.body.style.top = '';
window.scrollTo(0, parseInt(scrollY || '0') * -1);

According to this question+answer, it should be possible to address document and window in this way, but in my case it doesn't appear to do anything.