Apparently, the plugin is bugged : looking for a file with full path without any slash or backslash …
My local config and the apache log

Current LOCAL configuration :
– PHP/MySQL version : 7.2.3 / 5.7.17
– Webhost : Apache/2.4.25 (Win64) OpenSSL/1.0.2k PHP/7.2.3

[php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: startScan: , referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.642778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: timeout: 0, referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.642778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: scan status: , referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.652778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: Generating directory list., referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.822778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: 3 plugins left to process., referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.822778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: Processing: DashPress, referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.822778 2020] [php7:notice] [pid 4320:tid 1012] [client 127.0.0.1:51051] WPE PHP Compatibility: Attempted scan count: 1, referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test
[Tue May 26 01:17:54.942778 2020] [php7:error] [pid 4320:tid 1012] [client 127.0.0.1:51051] PHP Fatal error:  
Uncaught PHP_CodeSniffer_Exception: Source file D:webserverDocumentswpwp-contentpluginsdashpress/ does not exist in D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\vendor\\squizlabs\\php_codesniffer\\CodeSniffer.php:1740\nStack trace:
#0 D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\vendor\\squizlabs\\php_codesniffer\\CodeSniffer.php(653): PHP_CodeSniffer->processFile('D:webserverDocu...', NULL)
#1 D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\vendor\\squizlabs\\php_codesniffer\\CodeSniffer\\CLI.php(998): PHP_CodeSniffer->processFiles(Array, false)
#2 D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\src\\wpephpcompat.php(298): PHP_CodeSniffer_CLI->process(Array)
#3 D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\src\\wpephpcompat.php(242): WPEPHPCompat->process_file('D:webserverDocu...')
#4 D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\wpengine-phpcompat.php(180): WPEPHPCompat->sta in D:\\webserver\\Documents\\wp\\wp-content\\plugins\\php-compatibility-checker\\vendor\\squizlabs\\php_codesniffer\\CodeSniffer.php on line 1740, referer: http://127.0.0.1/wp/wp-admin/admin-ajax.php?action=wpephpcompat_start_test