Decrepation error

Hello,

I am using the plugin BackWPup on a testing site, where I have WP-DEBUG on set to true. As such, today I noticed the following error on my site:

Deprecated: Non-static method BackWPup_Admin::admin_css() should not be called statically in /var/www/vhosts/website.com/wp-includes/class-wp-hook.php on line 287

Debug info:
WordPress version: 5.4.2
BackWPup version: 3.7.1
PHP version: 7.3.5 (64bit)
MySQL version: 5.5.64-MariaDB-1~trusty
cURL version: 7.35.0
cURL SSL version: OpenSSL/1.0.1f
WP-Cron url: https://website.com/wp-cron.php
Server self connect: Response-test oké
Document root: /var/www/vhosts/website.com
Temp folder: /var/www/vhosts/website.com/wp-content/uploads/backwpup-578b85-temp/
Log folder: /var/www/vhosts/website.com/wp-content/uploads/backwpup-578b85-logs/
Server: Apache
Operating System: Linux
PHP SAPI: cgi-fcgi
Maximum execution time: 600 seconds
BackWPup maximum script execution time: 30 seconds
Alternative WP Cron: Off
Disabled WP Cron: Off
CHMOD Dir: 0755
Server Time: 11:32
Blog Time: 13:32
Blog Timezone: Europe/Amsterdam
Blog Time offset: 2 hours
Blog language: nl
MySQL-client encoding: utf8
PHP Memory limit: 256M
WP memory limit: 40M
WP maximum memory limit: 256M
Memory in use: 6,00 MB
Disabled PHP-functions: opcache_get_status
Loaded PHP Extensions: Core, PDO, PDO_ODBC, Phar, Reflection, SPL, SimpleXML, Zend OPcache, bcmath, bz2, calendar, cgi-fcgi, ctype, curl, date, dba, dom, enchant, exif, fileinfo, filter, ftp, gd, gettext, gmp, hash, iconv, imagick, imap, intl, ionCube Loader, json, ldap, libxml, mbstring, mysqli, mysqlnd, odbc, openssl, pcntl, pcre, pdo_mysql, pdo_pgsql, pdo_sqlite, pgsql, posix, pspell, readline, redis, session, soap, sockets, sodium, sqlite3, standard, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xml, xmlreader, xmlrpc, xmlwriter, xsl, zip, zlib

Thank you in advance for any help you can offer.