iPhone won't connect to WiFi

Check -> see the following Apple articles:

Connect to Wi-Fi on your iPhone, iPad, or iPod touch

Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

If your iPhone, iPad, or iPod touch won't connect to a Wi-Fi network - Apple Support

Recommended settings for Wi-Fi routers and access points

Recommended settings for Wi-Fi routers and access points - Apple Support

If you need help with your Wi‑Fi password

If you need help with your Wi‑Fi password - Apple Support

If they are On, turn Off Hotspot & VPN.

Marina ~ 64% maximum capacity is not healthy. Have the weak battery replaced and you'll then be able to connect with Wi-Fi:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

(Articles found by searching Apple's Knowledge Base.)

õ¿õ¬

Marina ~ Please tap on this Settings app icon:

...and scroll down to Battery and tap on it. Now perhaps this will make sense:

What's the Maximum Capacity % here?...

Settings > Battery > Battery Health

õ¿õ¬

Marina ~ Does your iPhone 8 Plus still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

õ¿õ¬