The Events Calendar: Community Events: Limit image upload to 3 megabytes.

functions.php

<?php

/**
 * The Events Calendar: Community Events: Limit image upload to 3 megabytes.
 *
 * Requires Community Events version 4.5.12 or later.
 *
 * @see Tribe__Events__Community__Main::max_file_size_allowed
 * @see wp_convert_hr_to_bytes()
 *
 * @link https://gist.github.com/cliffordp/03ddb4913adcdb7d2888ef6a7c7841c9 This snippet.
 * @link https://cl.ly/403L0o473b1P 1-minute video demonstrating this snippet works.
 *
 * @return int
 */
function cliff_ce_max_upload_size() {
	return wp_convert_hr_to_bytes( '3M' );
}

add_filter( 'tribe_community_events_max_file_size_allowed', 'cliff_ce_max_upload_size' );