Slow queries constantly getting stuck on Wordpress database of ~100,000 posts

I am constantly getting stuck SELECT queries on my wordpress databases like the following: https://i.stack.imgur.com/grZs3.png
Many of the SELECT queries that get stuck are fairly ordinary, such as pulling the last 10 posts of an author or pulling 10 posts in a category - these are normal Wordpress core queries that should run in a split second. My Wordpress databases that get afflicted with this have around 100,000 rows in the wp_posts table, with a size of around 1GB. This is an example of the largest tables from one of the databases: https://i.stack.imgur.com/vXtYy.png
My dedicated server has 4 CPU cores @ 3.4 GHz and 8 GB DDR4 RAM. For this server and these databases, should these kinds of issues be happening? What can I do to make normal Wordpress queries always run without getting stuck? I have tried changing from MyISAM to InnoDB with no effect, as well as changing different settings in my.cnf - here it is currently: [mysqld] pid-file = /var/run/mysqld/mysqld.pid log-error=/var/lib/mysql/errorlog.err performance-schema=0 default-storage-engine=MyISAM max_allowed_packet=268435456 open_files_limit=10000 slow_query_log=ON log_slow_verbosity=1 innodb_buffer_pool_size=1G aria_pagecache_buffer_size=512M query_cache_size=0 query_cache_type=0 query_cache_limit=0 join_buffer_size=512K tmp_table_size=32M max_heap_table_size=32M table_definition_cache=1200
And the result of running