You might want to ask for an invite to SGP as they have some groups dedicated to mid/rear-pack.
Otherwise, we do some races here every Sunday in GT3 and Wednesday with various combos. Beginners are welcome. We usually have a range of skill levels, so you will probably find yourself racing against someone.
e.g. https://www.racedepartment.com/threads/gt3-brands-hatch-sunday-10th-january-2021.195895/