AdGuard not working properly in any browsers on Solus 4.1 Fortitude

### Prerequisites

Please answer the following questions for yourself before submitting an issue. **YOU MAY DELETE THE PREREQUISITES SECTION.**

- [x] I am running the latest version
- [ ] I checked the documentation and found no answer
- [ ] I checked to make sure that this issue has not already been filed

### Issue Details

- **AdGuard version:**
- v3.4.31
- **Browser and version:**
- Firefox 79.0, Brave 1.11.101, and Google Chrome 84.0.4147.105
- **Operating system and version:**
- Solus 4.1 Fortitude (Linux)
- **Filters you use in AdGuard:**
- default
- **Stealth Mode settings:**
- disabled
- **Other browser extensions:**
- none

### Expected Behavior

When you go to filters and try to add a custom filter it's expected to allow you to add the filter

### Actual Behavior

It can't add the custom filter giving you an error

### Screenshots

Screenshots:

https://imgur.com/a/kS9iI6Q

### Additional Information

Didn't add Brave to the screenshots because I've got other extensions and made it my main browser now