Hi @Anonymous ,
What formula expression do you use now?
If you just get the warning it is just warning, not the error.
More details about delegation:
understand delegation in cavas-app
I test on my side also has the delegation(as App test1):
Filter('20190226filtermultipleperson',User().FullName in ShowColumns(PersonM,"DisplayName")) (‘20190226filtermultipleperson’ is my sp list name)
If you do not want the delegation warning, you could try to use the collection to collect your data firstly,and then filter.(As App test2)
App test1:

App test2:
Add one button control and then Button5.OnSelect: ClearCollect(test,'20190226filtermultipleperson')
And then Gallery3.Items: Filter(test,User().FullName in PersonM.DisplayName)

Hope this can be helpful.
Best Regards.
Yumia