TypeError: Cannot read properties of null (reading 'getVueInspector') in standalone devtools

[viliam-durina]

Due to company restrictions, I cannot install any browser plugins. Therefore I'm trying to set up standalone devtools as described in https://devtools.vuejs.org/guide/installation.html#standalone
However I'm getting this error:

(index):31 Uncaught (in promise) TypeError: Cannot read properties of null (reading 'getVueInspector')
    at (index):31:66345
    at (index):31:60962
    at (index):31:19571
    at Array.map (<anonymous>)
    at Object.emit ((index):31:19555)
    at Gs._emit ((index):31:60029)
    at (index):31:59920
    at _.<anonymous> ((index):31:68909)
    at O.emit ((index):2:5512)
    at _.value ((index):2:37542)

(index) is the script downloaded from http://localhost:8098/. I'm including the vue.js code using a <script> element, I'm using vue 2.7.16. Google gives zero results for getVueInspector, so I assume I'm doing something wrong. What could that be?