Not enough rep to comment so posting here. I agree with mustaccio - "Acceptable" is far too subjective.
"could this potentially affect SQL Server's read/write performance?"
yes. Here are some things to consider:
1 - The type of file(s) matters in context of performance. Files which are often read/written to will of course share the resources with the SQL Server files. Files which aren't being accessed when SQL Server files are being accessed won't noticeably affect performance.
2 - The type of storage matters. Shared IO has more severe performance consequence on spinning disk storage than SSD.
The idea is similar to the "Placing both data AND log files on the same device can cause contention for that device, resulting in poor performance. Placing the files on separate drives allows the I/O activity to occur at the same time for both the data and log files." as stated in Microsoft docs. Read placing any two files with simultaneous IO demand on the same device can cause contention for that device, resulting in poor performance.
Will it cause poor performance? Far too many variables to take into consideration such as storage specs & config, workload patterns of both SQL Server and w/e is sharing its resources, etc. to have concrete answer.
