My village website just fell victim to this problem as well. So I had to identify the problem in order to get the website into a state where I could do anything at all.
The site error.log file showed “PHP Parse error: syntax error, unexpected ‘)’, expecting variable (T_VARIABLE) in …/wp-content/plugins/ultimate-blocks/includes/ultimate-blocks-styles-css-generator.php on line 155”. All I did was to move the Ultimate Blocks plugin directory out of the way (thereby disabling it).
A very quick inspection showed that all that was needed was to remove the trailing comma off the parameter list of the get_background_colour_var() function. That’s all it took.
If any one else needs a quick fix… here it is!
Chris